Light-emitting device

ABSTRACT

A light-emitting device includes a base and a light-emitting element that is disposed on the base. The light-emitting element is made up of a plurality of semiconductor layers including a light-emitting layer, and at the same time, is covered with a wavelength converting portion that includes a wavelength converting material. The light-emitting layer emits primary light, and the wavelength converting material absorbs part of the primary light and emits secondary light. The luminance of the primary light emitted from the edge portion of the light extraction surface of the light-emitting device is higher than the luminance of the primary light emitted from the inner region located inside the edge portion, and the ratio of the primary light and the secondary light that are emitted from a light extraction surface of the wavelength converting portion is substantially uniform across the light extraction surface of the wavelength converting portion. Thereby, a light color difference across the light extraction surface of the wavelength converting portion that covers the light-emitting element can be reduced further, and it is possible to irradiate an irradiation surface with light of uniform color.

TECHNICAL FIELD

The present invention relates to a light-emitting device that includes alight-emitting element such as a light-emitting diode (hereinafterreferred to as an “LED”).

BACKGROUND ART

LEDs are not only compact and highly efficient as compared to existinglight sources that utilize electric discharge or radiation, but recentlyalso are gaining an increased luminous flux. LEDs thus are expected toreplace the existing light sources soon. Furthermore, because LEDs aremore compact than light sources that utilize electric discharge orradiation, they have the following advantages: they have a wider rangeof applications, are easier to handle and are available in variousdesigns as required. Accordingly, LEDs are considered as value-addedlight sources.

Light sources for lighting applications are required to have, as one ofthe characteristics, color uniformity, that is, no light colordifference depending on the emitting direction of light emitted. In alight-emitting device that includes a wavelength converting materialsuch as a fluorescent material, primary light emitted from thelight-emitting element and secondary light obtained through absorptionand conversion of the primary light by the wavelength convertingmaterial are combined, and light such as white light is emitted. In thiscase, the resulting color differs depending on the mixing ratio of theprimary light and the secondary light. This mixing ratio may differdepending on the emitting direction, which causes a light colordifference depending on the emitting direction, and a light colordifference across the light-emitting surface (light extraction surface)of the wavelength converting portion.

The following methods have been proposed for suppressing such lightcolor difference.

First, a method has been proposed in which a wavelength convertingportion (a resin layer that includes fluorescent material particles) isformed on an LED chip serving as a light-emitting element uniformly overthe shape of the LED chip (see, for example, Patent Document 1). Withthis configuration, the distance over which primary light passes throughthe wavelength converting portion can be made uniform, as compared to aconfiguration in which the wavelength converting portion is formed onthe LED chip by dripping or the like, and it is therefore possible tosuppress the light color difference in the light extraction surface ofthe wavelength converting portion.

Light sources for lighting applications that provide a high luminousflux are required to emit light of uniform color to the irradiationsurface. Accordingly, a further reduction in the light color differenceacross the light extraction surface of the wavelength converting portionis necessary.

Inorganic fluorescent material particles, which usually are used as awavelength converting material, are known to have a reflection functionin addition to the wavelength converting function, so that a scatteringaction is effected, and as a result, primary light and secondary lightare scattered, which can suppress the light color difference (see, forexample, Patent Document 2).

Another method has been proposed in which the vicinity of the center ofa wavelength converting portion that includes a wavelength convertingmaterial, that is, the area directly above a light-emitting element, ismade thick and the periphery of the wavelength converting portion ismade thin (see, for example, Patent Document 3). Patent Document 3states that “by reducing a light path length difference across thewavelength converting portion between primary light that travels in thevertically upward direction from the light-emitting element and primarylight that travels in an obliquely upward direction from thelight-emitting element, the ratio between the primary light and thesecondary light becomes substantially equal, and thus colornonuniformity is reduced”. This is based on the model that “if thedistribution of the wavelength converting material in the wavelengthconverting portion is uniform, the light path length has a correlationwith the frequency at which primary light hits the wavelength convertingmaterial, and the ratio between the primary light and the secondarylight is determined based on this frequency”.

Another method has been proposed in which the vicinity of the center ofa wavelength converting portion that includes a wavelength convertingmaterial, that is, the area directly above a light-emitting element, iscaused to have a higher concentration of the wavelength convertingmaterial than that of the periphery of the wavelength converting portion(see, for example, Patent Document 4). This is based on the model that“if the thickness of the wavelength converting portion is uniform, byreducing a difference in frequency at which light hits the wavelengthconverting material of the wavelength converting portion between primarylight that travels in the vertically upward direction from thelight-emitting element and primary light that travels in an obliquelyupward direction from the light-emitting element, the ratio between theprimary light and the secondary light becomes substantially equal, andthus color nonuniformity is reduced”.

-   Patent Citation 1: U.S. Pat. No. 6,468,821B2-   Patent Citation 2: JP H7-99345A-   Patent Citation 3: Japanese Patent No. 3065263 (paragraph [0016],    FIG. 2)-   Patent Citation 4: JP 2005-166733A (paragraph [0035], FIG. 8)

DISCLOSURE OF INVENTION Technical Problem

In the vicinity of the center of a wavelength converting portion,primary light that is substantially uniformly scattered comes from theperiphery of the vicinity of the center of the wavelength convertingportion. However, in the edge portion, the direction of scatteredprimary light is limited to a single direction, that is, from within tothe outer side of the wavelength converting portion. Because, in theedge portion, the primary light does not come from the externaldirection as described above, the mixed light emitted from the edgeportion of the wavelength converting portion lacks the primary lightcomponent. Consequently, a difference occurs in the mixing ratio ofprimary light and secondary light between the edge portion of the lightextraction surface of the wavelength converting portion and the innerregion thereof, and this leads to a light color difference across thelight extraction surface of the wavelength converting portion.

Ordinarily, the light intensity of light (primary light) emitted from alight-emitting element is high in the vertically upward direction of theemitting surface or in a direction slightly inclined from the verticallyupward direction (hereinafter these are referred to as a “substantiallyvertically upward direction”), and is smaller as it moves in the lateraldirection. In other words, the light intensity of the mixed light ofprimary light and secondary light that are mixed in the wavelengthconverting portion located in the substantially vertically upwarddirection of the light-emitting element is higher than that of the mixedlight of primary light and secondary light that are mixed in thewavelength converting portion located in a direction obliquely upwardfrom the lateral direction relative to the emitting surface. If theprimary light can be caused to enter a wavelength converting portionhaving a uniform thickness and a uniform distribution of a wavelengthconverting material at a uniform intensity from the undersurface of thewavelength converting portion, uniformly mixed light can be emitted fromthe upper surface of the wavelength converting portion.

By increasing the distance between the light-emitting element and thewavelength converting portion, the influence of the distribution oflight emitted from the light-emitting element in the light-emittingdirection is reduced, and thus primary light having a substantiallyuniform intensity is caused to enter the undersurface of the wavelengthconverting portion. Accordingly, the color nonuniformity due to thedistribution of light emitted from the light-emitting element iseliminated. However, in order to achieve a thin LED, the distancebetween the light-emitting element and the wavelength converting portionis made small, which increases the influence of the distribution oflight emitted from the light-emitting element in the light-emittingdirection, and becomes problematic when trying to achieve a thin LEDwith less color nonuniformity.

The present invention has been conceived in order to solve the aboveproblem encountered in conventional technology, and it is an object ofthe present invention to provide a light-emitting device that canirradiate an irradiation surface with light of uniform color.

Technical Solution

In order to achieve the above object, a light-emitting device accordingto the present invention is configured as follows. A light-emittingdevice includes a base, and a light-emitting element that is disposed onthe base and that emits primary light, wherein the light-emittingelement is covered with a wavelength converting portion that includes awavelength converting material that absorbs part of the primary lightand emits secondary light, and the light-emitting device comprises aprimary light intensity distribution control means for setting anintensity distribution of the primary light within the wavelengthconverting portion such that a mixing ratio of the primary light and thesecondary light that are emitted from a light extraction surface of thewavelength converting portion is substantially uniform.

According to the configuration of the light-emitting device, the primarylight intensity distribution control means is provided that sets theintensity distribution of the primary light within the wavelengthconverting portion such that mixed light of the primary light and thesecondary light emitted from the light extraction surface of thewavelength converting portion is substantially uniform, and it istherefore possible to provide a light-emitting device that can irradiatean irradiation surface with light of uniform color.

In the configuration of the light-emitting device according to thepresent invention, it is preferable that a luminance of the primarylight emitted from an edge portion of a light extraction surfaceprovided on one principal surface of the light-emitting element is sethigher than a luminance of the primary light emitted from an innerregion that is located inside the edge portion. According to thispreferred example, the luminance of the primary light emitted from theedge portion of the light extraction surface of the light-emittingelement is set higher than that of the primary light emitted from theinner region located inside the edge portion, whereby a light colordifference across the light extraction surface of the wavelengthconverting portion that covers the light-emitting element can beeliminated, and it is therefore possible to reduce the colornonuniformity of light extracted from the light-emitting device and toirradiate the irradiation surface with light of uniform color. In thiscase, it is preferable that the light-emitting element is divided intoat least two diodes: a diode in the edge portion and a diode in theinner region located inside the edge portion. The diode in the edgeportion and the diode in the inner region located inside the edgeportion are connected in series, and the light-emitting layer of thediode in the edge portion has an area smaller than the area of thelight-emitting layer of the diode in the inner region located inside theedge portion. According to this preferred example, because the currentdensity of the light-emitting layer of the diode in the edge portion canbe increased, it is possible to make the luminance of the primary lightemitted from the edge portion of the light extraction surface of thelight-emitting element higher than the luminance of the primary lightemitted from the inner region located inside the edge portion. In thiscase, it is preferable that the light-emitting element is divided intoat least two diodes: a diode in the edge portion and a diode in theinner region located inside the edge portion, and the diode in the edgeportion and the diode in the inner region located inside the edgeportion can be driven electrically independently of each other.According to this preferred example, a current can be injected such thatthe luminance of the primary light emitted from the edge portion of thelight extraction surface of the light-emitting element is higher thanthe luminance of the primary light emitted from the inner region locatedinside the edge portion. In this case, it is preferable that at leastone electrode of the light-emitting element is provided only in the edgeportion. According to this preferred example, the current density of theedge portion of the light-emitting element can be increased, and it istherefore possible to make the luminance of the primary light emittedfrom the edge portion of the light extraction surface of thelight-emitting element higher than the luminance of the primary lightemitted from the inner region located inside the edge portion. In thiscase, it is preferable that, in at least one electrode of thelight-emitting element, the electrode spacing in the edge portion issmaller than the electrode spacing in the inner region located insidethe edge portion. According to this preferred example, the currentdensity of the edge portion of the light-emitting element can beincreased, so that the luminance of the primary light emitted from theedge portion of the light extraction surface of the light-emittingelement becomes higher than the luminance of the primary light emittedfrom the inner region located inside the edge portion. In this case, itis preferable that, in at least one electrode, the electrode resistanceof the edge portion is smaller than the electrode resistance of theinner region located inside the edge portion. According to thispreferred example, the current density of the edge portion of thelight-emitting element can be increased, so that the luminance of theprimary light emitted from the edge portion of the light extractionsurface of the light-emitting element becomes higher than the luminanceof the primary light emitted from the inner region located inside theedge portion. In this case, it is preferable that, in the light-emittingelement, the internal resistance of the inner region located inside theedge portion is larger than the internal resistance of the edge portion.According to this preferred example, the current density of the edgeportion of the light-emitting element can be increased, so that theluminance of the primary light emitted from the edge portion of thelight extraction surface of the light-emitting element becomes higherthan the luminance of the primary light emitted from the inner regionlocated inside the edge portion. In this case, it is preferable that, inthe light-emitting element, the transmissivity of the primary lightemitted from the edge portion is larger than the transmissivity of theprimary light emitted from the inner region located inside the edgeportion. According to this preferred example, the luminance of theprimary light emitted from the edge portion of the light extractionsurface of the light-emitting element can be made higher than theluminance of the primary light emitted from the inner region locatedinside the edge portion.

In the configuration of the light-emitting device of the presentinvention, it is preferable that the wavelength converting portion has asubstantially uniform thickness, and a wavelength converting material isdispersed substantially uniformly.

In the configuration of the light-emitting device of the presentinvention, it is preferable that the light-emitting element is made upof a plurality of semiconductor layers including a light-emitting layerthat emits primary light.

In the configuration of the light-emitting device of the presentinvention, it is preferable that the light-emitting element is coveredwith a cover portion, the cover portion is covered with the wavelengthconverting portion, and the refractive index of at least a portion ofthe cover portion in the outer periphery of the wavelength convertingportion is set higher than the refractive index of the other portion ofthe cover portion.

In the configuration of the light-emitting device of the presentinvention, it is preferable that the light-emitting element is coveredwith a cover portion, the cover portion is covered with the wavelengthconverting portion, at least part of the cover portion includes ananoparticle material, and at least a portion of the cover portion inthe outer periphery of the wavelength converting portion includes ananoparticle material having a refractive index higher than that of thebase material of the cover portion.

In the configuration of the light-emitting device of the presentinvention, it is preferable that the light-emitting element is coveredwith a cover portion, the cover portion is covered with the wavelengthconverting portion, at least part of the cover portion includes ananoparticle material, and at least a portion of the cover portion inthe outer periphery of the wavelength converting portion includes ananoparticle material at a ratio higher than that of the other portionof the cover portion.

According to these preferred examples, due to the tendency for light toconcentrate on a portion having a high refractive index, the lightintensity of the primary light in the directions ranging from thelateral direction to the obliquely upward direction, where the coverportion having a high refractive index is located, is relativelyincreased, and thus, in the cover portion as a whole, the intensitydistribution of the primary light can be made uniform. In other words,the primary light can be caused to enter the wavelength convertingportion having a uniform thickness and a uniform distribution of thewavelength converting material at a uniform intensity from theundersurface of the wavelength converting portion. Consequently,uniformly mixed light (of primary light and secondary light that isobtained through absorption and conversion of the primary light by thewavelength converting material) can be emitted from the upper surface ofthe wavelength converting portion, and it is therefore possible toreduce the color nonuniformity of light extracted from thelight-emitting device.

In this case, it is preferable that the wavelength converting portion isformed into a dome shape. According to this preferred example, most ofthe light emitted from the light-emitting element is incident upon thewavelength converting portion perpendicularly to the wavelengthconverting portion, and it is therefore possible to prevent thereflection of light at the interface between the wavelength convertingportion and the cover portion. Thereby, the light extraction efficiencycan be improved further.

In this case, it is preferable that, in the wavelength convertingportion, the refractive index of a portion that is located above theportion of the cover portion having a high refractive index is higherthan the refractive index of the other part of the wavelength convertingportion. According to this preferred example, in addition to theabove-described effects, reflection at the interface between the coverportion and the wavelength converting portion can be reduced, and thus aloss caused by the reflection can be reduced. Furthermore, even in thewavelength converting portion, the intensity distribution can be madeuniform.

In this case, it is preferable that a space is provided between thecover portion and the wavelength converting portion. According to thispreferred example, heat from the light-emitting element can bedissipated with high efficiency.

In the configuration of the light-emitting device of the presentinvention, it is preferable that a plurality of the light-emittingelements are provided, and the plurality of light-emitting elements arecovered with the wavelength converting portion that is continuous, andare disposed such that a spacing between adjacent light-emittingelements is decreased from a center portion side of the base graduallytoward a periphery side thereof.

In the configuration of the light-emitting device of the presentinvention, it is preferable that a plurality of the light-emittingelements are provided, and the plurality of light-emitting elements arecovered with the wavelength converting portion that is continuous, andare disposed such that a mounting density of the light-emitting elementsper unit area of the wavelength converting portion is increased from acenter portion side of the base gradually toward a periphery sidethereof.

In the configuration of the light-emitting device of the presentinvention, it is preferable that a plurality of the light-emittingelements are provided, and the plurality of light-emitting elements arecovered with the wavelength converting portion that is continuous, andare disposed such that a light-emitting efficiency of the wavelengthconverting portion is increased from a center portion side of the basegradually toward a periphery side thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a light-emittingdevice according to Embodiment 1 of the present invention.

FIG. 2 schematically shows a light-emitting element that is used in thelight-emitting device according to Embodiment 1 of the presentinvention. FIG. 2( a) is a cross-sectional view, and FIG. 2( b) is aplan view showing a light extraction surface.

FIG. 3 shows how the light-emitting device according to Embodiment 1 ofthe present invention is used. FIG. 3( a) shows the case where a sealingmaterial is used, FIG. 3( b) shows the case where sealing gas is used,and FIG. 3( c) shows the case where sealing gas is used, and where thelight-emitting device is formed into a module.

FIG. 4 shows diagrams that more specifically show a light-emittingelement that is used in the light-emitting device according toEmbodiment 1 of the present invention. FIG. 4( a) is a cross-sectionalview, and FIG. 4( b) is a plan view showing a side opposite to the lightextraction surface.

FIG. 5 shows diagrams that more specifically show a light-emittingelement that is used in the light-emitting device according toEmbodiment 1 of the present invention. FIG. 5( a) is a cross-sectionalview, and FIG. 5( b) is a diagram showing the area ratio of alight-emitting layer.

FIG. 6 is a cross-sectional view that more specifically shows thelight-emitting device according to Embodiment 1 of the presentinvention.

FIG. 7 is a schematic diagram used to illustrate a method for measuringthe color temperature of light emitted from a light-emitting device inEmbodiments 1 and 8 of the present invention.

FIG. 8 is a graph showing the result obtained through the evaluation ofcolor nonuniformity of light emitted from the light-emitting deviceaccording to Embodiment 1 of the present invention.

FIG. 9 shows diagrams that more specifically show a light-emittingelement that is used in a light-emitting device according to Embodiment2 of the present invention. FIG. 9( a) is a cross-sectional view, andFIG. 9( b) is a plan view showing a side opposite to the lightextraction surface.

FIG. 10 shows diagrams that more specifically show a light-emittingelement that is used in a light-emitting device according to Embodiment3 of the present invention. FIG. 10( a) is a cross-sectional view, andFIG. 10( b) is a plan view showing a light extraction surface.

FIG. 11 is a cross-sectional view that more specifically shows thelight-emitting device according to Embodiment 3 of the presentinvention.

FIG. 12 shows diagrams that specifically show an example of alight-emitting element that is used in a light-emitting device accordingto Embodiment 4 of the present invention. FIG. 12( a) is across-sectional view, and FIG. 12( b) is a plan view showing a lightextraction surface.

FIG. 13 shows diagrams that specifically show another example of thelight-emitting element that is used in the light-emitting deviceaccording to Embodiment 4 of the present invention. FIG. 13( a) is across-sectional view, and FIG. 13( b) is a plan view showing a lightextraction surface.

FIG. 14 shows diagrams that specifically show an example of alight-emitting element that is used in a light-emitting device accordingto Embodiment 5 of the present invention. FIG. 14( a) is across-sectional view, and FIG. 14( b) is a plan view showing a lightextraction surface.

FIG. 15 shows diagrams that specifically show a light-emitting elementthat is used in a light-emitting device according to Embodiment 6 of thepresent invention. FIG. 15( a) is a cross-sectional view, and FIG. 15(b) is a plan view showing a light extraction surface.

FIG. 16 shows diagrams that specifically show an example of alight-emitting element that is used in a light-emitting device accordingto Embodiment 7 of the present invention. FIG. 16( a) is across-sectional view, and FIG. 16( b) is a plan view showing a lightextraction surface.

FIG. 17 shows diagrams that specifically show another example of thelight-emitting element that is used in the light-emitting deviceaccording to Embodiment 7 of the present invention. FIG. 17( a) is across-sectional view, and FIG. 17( b) is a plan view showing a lightextraction surface.

FIG. 18 is a schematic cross-sectional view showing an example of alight-emitting device according to Embodiment 8 of the presentinvention.

FIG. 19 shows enlarged cross-sectional views used to illustrate a methodfor mounting a light-emitting element according to an embodiment of thepresent invention.

FIG. 20 is a schematic cross-sectional view showing another example ofthe light-emitting device according to Embodiment 8 of the presentinvention.

FIG. 21 is a schematic cross-sectional view showing still anotherexample of the light-emitting device according to Embodiment 8 of thepresent invention.

FIG. 22 is a schematic cross-sectional view showing still anotherexample of the light-emitting device according to Embodiment 8 of thepresent invention.

FIG. 23 is a schematic cross-sectional view showing a specific exampleof the light-emitting device according to Embodiment 8 of the presentinvention.

FIG. 24 is a graph showing the result obtained through the evaluation ofcolor nonuniformity of light emitted from the light-emitting devices ofa specific example and a comparative example in Embodiment 8 of thepresent invention.

FIG. 25 is a schematic cross-sectional view showing an example of alight-emitting device according to Embodiment 9 of the presentinvention.

FIG. 26 is a schematic cross-sectional view showing another example ofthe light-emitting device according to Embodiment 9 of the presentinvention.

FIG. 27 is a schematic cross-sectional view showing still anotherexample of the light-emitting device according to Embodiment 9 of thepresent invention.

FIG. 28 is a schematic cross-sectional view showing still anotherexample of the light-emitting device according to Embodiment 9 of thepresent invention.

FIG. 29 is a schematic cross-sectional view showing an example of alight-emitting device according to Embodiment 10 of the presentinvention.

FIG. 30 is a schematic cross-sectional view showing another example ofthe light-emitting device according to Embodiment 10 of the presentinvention.

FIG. 31 is a schematic cross-sectional view showing still anotherexample of the light-emitting device according to Embodiment 10 of thepresent invention.

FIG. 32 is a schematic cross-sectional view showing an example of alight-emitting device according to Embodiment 11 of the presentinvention.

FIG. 33 is a schematic cross-sectional view showing another example ofthe light-emitting device according to Embodiment 11 of the presentinvention.

FIG. 34 is a plan view showing an example of a light-emitting deviceaccording to Embodiment 12 of the present invention.

EXPLANATION OF REFERENCE

1 Light-Emitting Device

2 Base

3 Light-Emitting Element

4 Wavelength Converting Portion

5 Light Extraction Surface of Light-Emitting Element

5 a Edge Portion of Light Extraction Surface of Light-Emitting Element

5 b Inner Region Located inside Edge Portion of Light Extraction Surfaceof Light-Emitting Element

6 Light Extraction Surface of Wavelength Converting Portion

34, 52, 53, 54 Light-Emitting Device

35, 35 a Base

36, 36 f, 36 g, 36 h, 36 i, 36 j, 36 k Light-Emitting Element

37, 37 a, 37 b, 37 c First Cover Portion

38, 38 a, 38 b, 38 c Second Cover Portion

39, 39 a, 39 b Wavelength Converting Portion

40, 40 a Space

41 Cover Portion

60 Base

61 Light-Emitting Element

62 Wavelength Converting Portion

63 Light-Emitting Device

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in further detailwith reference to embodiments.

Embodiment 1

A light-emitting device according to Embodiment 1 of the presentinvention will be described first with reference to FIGS. 1 to 6. FIG. 1is a schematic cross-sectional view showing the light-emitting deviceaccording to the present embodiment. FIG. 2 schematically shows alight-emitting element that is used in the light-emitting deviceaccording to the present embodiment. FIG. 2( a) is a cross-sectionalview, and FIG. 2( b) is a plan view showing a light extraction surface.FIG. 3 shows how the light-emitting device according to the presentembodiment is used. FIG. 3( a) shows the case where a sealing materialis used, FIG. 3( b) shows the case where sealing gas is used, and FIG.3( c) shows the case where sealing gas is used, and where thelight-emitting device is formed into a module. FIG. 4 shows diagramsthat more schematically show a light-emitting element that is used inthe light-emitting device according to the present embodiment. FIG. 4(a) is a cross-sectional view, and FIG. 4( b) is a plan view showing aside opposite to the light extraction surface. FIG. 5 shows diagramsthat more specifically show a light-emitting element that is included inthe light-emitting device according to the present embodiment. FIG. 5(a) is a cross-sectional view, and FIG. 5( b) is a diagram showing thearea ratio of a light-emitting layer. FIG. 6 is a cross-sectional viewthat more specifically shows the light-emitting device according to thepresent embodiment.

As shown in FIG. 1, a light-emitting device 1 according to the presentembodiment includes a flat plate-like base 2, and a singlelight-emitting element 3 that is disposed on the base 2. Thelight-emitting element 3 is made up of a plurality of semiconductorlayers including a light-emitting layer, and is covered tightly with awavelength converting portion 4 that includes a wavelength convertingmaterial. The wavelength converting portion 4 has a uniform thickness,and the wavelength converting material is uniformly dispersed.

The light-emitting layer of the light-emitting element 3 emits primarylight, and the wavelength converting material of the wavelengthconverting portion 4 absorbs the primary light and then emits secondarylight.

As shown in FIGS. 2( a) and 2(b), the light-emitting element 3 isconfigured such that the luminance of primary light emitted from an edgeportion 5 a of a light extraction surface 5 is higher than the luminanceof primary light emitted from an inner region 5 b that is located insidethe edge portion 5 a. Thereby, the mixing ratio of the primary light andthe secondary light that are emitted from a light extraction surface 6(see FIG. 1) of the wavelength converting portion 4 becomessubstantially uniform across the light extraction surface 6 of thewavelength converting portion 4. In other words, the light-emittingdevice 1 of the present embodiment includes a primary light intensitydistribution control means for setting the intensity distribution of theprimary light within the wavelength converting portion 4 such that themixing ratio of the primary light and the secondary light that areemitted from the light extraction surface 6 of the wavelength convertingportion 4 is substantially uniform.

According to the light-emitting device 1 of the present embodiment,because the light-emitting element 3 is configured such that theluminance of primary light emitted from the edge portion 5 a of thelight extraction surface 5 is higher than the luminance of primary lightemitted from the inner region 5 b located inside the edge portion 5 a, alight color difference across the light extraction surface 6 of thewavelength converting portion 4 that covers the light-emitting element 3can be eliminated, and it is therefore possible to irradiate theirradiation surface with light of uniform color.

The material constituting the base 2 is not limited to a particularmaterial, and it is possible to use, for example, monocrystals such assapphire, Si, GaN, AlN, ZnO, SiC, BN and ZnS; ceramics such as Al₂O₃,AlN, BN, MgO, ZnO, SiC and C, and mixtures thereof; metals such as Al,Cu, Fe, Au and W, and alloys that include these metals; glass epoxy;resins such as epoxy resin, silicone resin, acrylic resin, urea resin,amide resin, imide resin, polycarbonate resin, polyphenyl sulfide resin,liquid crystal polymer, acrylonitrile-butadiene-styrene resin (ABSresin), methacrylate resin (PMMA resin) and cyclic olefin copolymer, andmixtures thereof. These materials also may be used as materials for agrowth substrate of the light-emitting element 3. Accordingly, the base2 may also serve as a growth substrate of the light-emitting element 3.Other than a configuration in which a film epitaxially grown on a growthsubstrate, which is made of sapphire, SiC, GaN, Si or the like, of thelight-emitting element 3 is disposed on the base 2, a configuration todispose the light-emitting element 3 on the base 2 such that this growthsubstrate does not remain can be used.

There is no particular limitation on the configuration and mountingmethod of the light-emitting element 3. Examples of the configuration ofthe base include a lead frame base, a package base in which alight-emitting element is mounted, and a submount base that isinterposed between a light-emitting element and a package base. As thelight-emitting element 3, it is possible to use, for example, a greenLED that emits green light having a wavelength of 500 to 550 nm, a blueLED that emits blue light having a wavelength of 420 to 500 nm, ablue-violet LED that emits blue-violet light having a wavelength of 380to 420 nm, and an ultraviolet LED having an even shorter wavelength. Inthe case of a nitride semiconductor material, it is represented by ageneral formula: B_(z)Al_(x)Ga_(1-x-y-z)In_(y)N (where x is in the rangeof 0 to 1, y is in the range of 0 to 1, z is in the range of 0 to 1, andx+y+z is in the range of 0 to 1). Hereinafter, this is referred to as“GaN-based semiconductor”. It is also possible to use a II-VI groupsemiconductor material such as ZnS or ZnO.

The light-emitting element is not limited to those made of a compoundsemi-conductor material, and it is also possible to use, for example, alight-emitting element made of an organic semiconductor material orinorganic semiconductor material.

The wavelength converting portion 4 is made of, for example, awavelength converting material, and a light-transmitting materialserving as a base material for dispersing the wavelength convertingmaterial.

As the wavelength converting material, for example, a fluorescentmaterial can be used. As the fluorescent material, it is possible touse, for example, a red fluorescent material that emits red light, anorange fluorescent material that emits orange light, a yellowfluorescent material that emits yellow light, a green fluorescentmaterial that emits green light, and so on. As the red fluorescentmaterial, it is possible to use, for example, a silicate-based materialsuch as Ba₃MgSi₂O₈:Eu²⁺, Mn²⁺, a nitridosilicate-based material such asSr₂Si₅N₈:Eu²⁺, a nitridoaluminosilicate-based material such asCaAlSiN₃:Eu²⁺, an oxonitridoaluminosilicate-based material such asSr₂Si₄AlON₇:Eu²⁺, a sulfide-based material such as (Sr, Ca)S:Eu²⁺,La₂O₂S:Eu³⁺, and so on. As the orange fluorescent material, it ispossible to use, for example, a silicate-based material such as (Sr,Ca)₂SiO₄:Eu²⁺, a garnet-based material such as Gd₃Al₅O₁₂:Ce³⁺, aCa-alpha-sialon-based material such as Ca-alpha-SiAlON:Eu²⁺, and so on.As the yellow fluorescent material, it is possible to use, for example,a silicate-based material such as (Sr, Ba)₂SiO₄:Eu²⁺, a garnet-basedmaterial such as (Y, Gd)₃Al₅O₁₂:Ce³⁺, a sulfide-based material such asCaGa₂S₄:Eu²⁺, a Ca-alpha-sialon-based material such asCa-alpha-SiAlON:Eu²⁺, and so on. As the green fluorescent material, itis possible to use, for example, an aluminate-based material such asBaMgAl₁₀O₁₇:Eu²⁺, Mn²⁺ or (Ba, Sr, Ca)Al₂O₄:Eu²⁺, a silicate-basedmaterial such as (Ba, Sr)₂SiO₄:Eu²⁺, a Ca-alpha-sialon-based materialsuch as Ca-alpha-SiAlON:Yb²⁺, a beta-sialon-based material such asbeta-Si₃N₄:Eu²⁺, an oxonitridoaluminosilicate-based material such as(Ba, Sr, Ca)₂Si₄AlON₇:Ce³⁺, a sulfide-based material such asSrGa₂S₄:Eu²⁺, a garnet-based material such as Y₃(Al, Ga)₅O₁₂:Ce³⁺,Y₃Al₅O₁₂:Ce³⁺, Ca₃Sr₂Si₃O₁₂:Ce³⁺ or BaY₂SiAl₄O₁₂:Ce³⁺, an oxide-basedmaterial such as CaSc₂O₄:Ce³⁺, and so on. The light emitted from theupper surface of the wavelength converting portion is not limited towhite light, and fine light color designs are possible by selectingthese fluorescent materials as appropriate. And infinite variations arepossible by using a plurality of different types of fluorescentmaterials having different luminous wavelengths. Other than theconfiguration in which the wavelength converting material is disperseduniformly in the wavelength converting portion, the wavelengthconverting portion can have, for example, a configuration in which theconcentration of the wavelength converting material is changed from theundersurface of the wavelength converting portion substantiallygradually toward the upper surface thereof, a configuration in whichlayers made of different wavelength converting materials are laminated,a configuration in which cells made of different wavelength convertingmaterials are arranged in a matrix form, or the like. With any of theabove-described configurations, uniformly mixed light can be emittedfrom the upper surface of the wavelength converting portion by causingprimary light to enter the undersurface of the wavelength convertingportion at a uniform intensity.

As the light-transmitting material, any material can be used as long asit allows the light extracted from the light-emitting device 1 to passtherethrough. Examples thereof include resins such as epoxy resin,silicone resin, acrylic resin, urea resin, amide resin, imide resin,polycarbonate resin, polyphenyl sulfide resin, liquid crystal polymer,ABS resin, PMMA resin and cyclic olefin copolymer; resins made of amixture thereof; glass that is formed by the sol-gel method using metalalkoxide or colloidal silica as a starting material; and glass such aslow melting point glass. It is also possible to use a composite materialobtained by dispersing metal oxide particles in the light-transmittingmaterial serving as a base material. When a curable resin is used as thebase material, the thixotropy of the curable resin before being curedcan be improved by dispersing the metal oxide particles in the curableresin in an uncured state, so that the wavelength converting portion 4can be formed easily into a desired shape. Furthermore, because the heatconductivity is improved as compared to the case of using a resin alone,heat from the light-emitting element 3 can be dissipated with highefficiency.

When a blue-violet LED or ultraviolet LED is used as the light-emittingelement 3, for example, the above-described fluorescent material may becombined with a blue fluorescent material that emits blue light or ablue-green fluorescent material that emits blue-green light. As the bluefluorescent material, it is possible to use, for example, analuminate-based material such as BaMgAl₁₀O₁₇:Eu²⁺, a silicate-basedmaterial such as Ba₃MgSi₂O₈:Eu²⁺, a halophosphate-based material such as(Sr, Br)₁₀(PO₄)₆Cl₂:Eu²⁺, and so on. As the blue-green fluorescentmaterial, it is possible to use, for example, an aluminate-basedmaterial such as Sr₄Al₁₄O₂₅:Eu²⁺, a silicate-based material such as Sr₂Si₃O₈-2SiCl₂:Eu²⁺, and so on.

When actually using the above-described light-emitting device 1, forexample, as shown in FIG. 3( a), the light-emitting device 1 is disposedat the bottom of a recess of the base 55, and the recess is filled witha sealing material 56. Alternatively, as shown in FIG. 3( b), thelight-emitting device 1 may be disposed on the upper surface of a flatplate-like base 57, and a sealing gas 58 may be filled around thelight-emitting device 1. Alternatively, as shown in FIG. 3( c), aplurality of light-emitting devices 1′, each of which includes alight-emitting element 3 and a wavelength converting portion 4, may bedisposed on the upper surface of a flat plate-like base 57, and asealing gas 58 may be filled around each light-emitting device 1′ toform a light-emitting module.

As the sealing material 56, it is possible to use, for example, resinssuch as epoxy resin, silicone resin, acrylic resin, urea resin, amideresin, imide resin, polycarbonate resin, polyphenyl sulfide resin,liquid crystal polymer, ABS resin, PMMA resin and cyclic olefincopolymer; resins made of a mixture of these resins; glass that isformed by sol-gel method using metal alkoxide or colloidal silica as astarting material; or glass such as low melting point glass.

As the sealing gas 58, for example, an inert gas, such as nitrogen orargon, or dry air can be used.

Hereinafter, the light-emitting device 1 of the present embodiment and alight-emitting element 3 that can be used in the light-emitting device 1will be described in further detail with reference to FIGS. 4 to 6.

As shown in FIGS. 4( a) and 4(b), a GaN semi-insulating layer 8 isformed on one principal surface of a growth substrate 7 made of GaN,SiC, sapphire or the like, and an n-GaN-based semiconductor layer 9, alight-emitting layer 10, and a p-GaN-based semiconductor layer 11 arelaminated in this order on the GaN semi-insulating layer 8. The otherprincipal surface (light extraction surface 5) of the growth substrate 7is processed to have an uneven structure. Thereby, the light extractionefficiency of the light-emitting device can be improved.

An isolation groove 12 for separating the light-emitting element 3 intoa portion corresponding to the edge portion 5 a of the light extractionsurface 5 and a portion corresponding to the inner region 5 b locatedinside the edge portion 5 a is provided such that the isolation groove12 spans across the n-GaN-based semiconductor layer 9, thelight-emitting layer 10, the p-GaN-based semiconductor layer 11, andpart of the GaN semi-insulating layer 8. Thereby, the light-emittingelement 3 is divided into two diodes: a diode in the edge portion and adiode in the inner region located inside the edge portion.

A Rh/Pt/Au electrode 13 which is a highly reflective electrode isprovided as an anode electrode on the p-GaN-based semiconductor layer 11at the edge portion and the inner region located inside the edgeportion, and the Rh/Pt/Au electrode 13 of the edge portion iselectrically connected to an anode terminal 14. Likewise, a Ti/Auelectrode 15 serving as a cathode electrode is provided in then-GaN-based semi-conductor layer 9 at the edge portion and the innerregion located inside the edge portion, and the Ti/Au electrode 15 ofthe inner region located inside the edge portion is electricallyconnected to a cathode terminal 16.

The Ti/Au electrode 15 of the edge portion as a cathode electrode andthe Rh/Pt/Au electrode 13 of the inner region located inside the edgeportion as an anode electrode are connected electrically via a wiringlayer 17. Thereby, as shown in FIG. 4( b), the diode D1 of the edgeportion and the diode D2 of the inner region located inside the edgeportion are connected in series.

In the present embodiment, the light-emitting element 3 is disposed onthe base 2 such that the growth substrate 7 remains, but a configurationmay be employed in which the light-emitting element 3 is disposed on thebase 2 such that the growth substrate 7 does not remain, as in anembodiment described later.

An insulating layer 18 made of silicon nitride is interposed between theanode terminal 14 and the wiring layer 17, between the wiring layer 17and the n-GaN-based semiconductor layer 9, light-emitting layer 10 andp-GaN-based semiconductor layer 11, and between the cathode terminal 16and the wiring layer 17, n-GaN-based semi-conductor layer 9,light-emitting layer 10 and p-GaN-based semiconductor layer 11.

As the electrode material, Ag, Al, Au, Ni, Rh, Pd, Pt, Ti, W, Cu, oralloys that are made thereof, ITO (indium tin oxide), ZnO and so on canbe used.

The light-emitting element 3 of the present embodiment has theabove-described configuration. As shown in FIGS. 5( a) and 5(b), in thelight-emitting element 3 of the present embodiment, the area of thelight-emitting layer 10 of the diode in the edge portion is smaller thanthe area of the light-emitting layer 10 of the diode in the inner regionlocated inside the edge portion. More specifically, the light-emittinglayer 10 of the diode in the edge portion has an outer peripheral sizeof about 0.9 mm*about 0.9 mm, and the light-emitting layer 10 of thediode in the inner region located inside the edge portion has an outerperipheral size of about 0.6 mm*about 0.6 mm. Consequently, the ratiobetween the area of the light-emitting layer 10 of the diode in the edgeportion and the area of the light-emitting layer 10 of the diode in theinner region located inside the edge portion is approximately 2:3. Inother words, if the isolation groove 12 and the like are not considered,the area of the light-emitting layer 10 of the diode in the edge portionis 0.45 mm², and the area of the light-emitting layer 10 of the diode inthe inner region located inside the edge portion is 0.36 mm². However,if the fact that the light-emitting layer 10 is removed in the shape ofa circle having a diameter of 0.2 mm at the location of the cathodeterminal 16, as well as the isolation width of each diode, isconsidered, the ratio is approximately 2:3. The edge portion 5 a (highluminance region) of the light extraction surface 5 has a width of about0.15 mm.

As described above, the light-emitting element 3 of the presentembodiment is divided into two diodes: a diode in the edge portion and adiode in the inner region located inside the edge portion, the diode inthe edge portion and the diode in the inner region located inside theedge portion are connected in series, and the area of the light-emittinglayer 10 of the diode in the edge portion is smaller than that of thelight-emitting layer 10 of the diode in the inner region located insidethe edge portion. Thereby, the current density of the light-emittinglayer 10 of the diode in the edge portion can be increased, and thus theluminance of the primary light emitted from the edge portion 5 a of thelight extraction surface 5 of the light-emitting element 3 will behigher than the luminance of the primary light emitted from the innerregion 5 b located inside the edge portion 5 a.

As shown in FIG. 6, the light-emitting element 3 is mounted on the base2 by causing the anode terminal 14 and the cathode terminal 16 to adhereto an Au/Sn adhesion layer (not shown). The Au/Sn adhesion layer iselectrically connected to a Ti/Pt/Au electrode 19 disposed on the base2. The light-emitting element 3 is covered with a wavelength convertingportion 4 in a tight contact state.

The light-emitting device 1 of the present embodiment has theabove-described configuration. In the present embodiment, the height ofthe light-emitting element 3 is about 30 micrometer, and the height ofthe wavelength converting portion 4 (the height from the surface of thebase 2) is about 0.2 mm. Because a configuration is adopted in which theluminance of the primary light emitted from the edge portion 5 a of thelight extraction surface 5 of the light-emitting element 3 is madehigher than the luminance of the primary light emitted from the innerregion 5 b located inside the edge portion 5 a as described above, thelight color difference across the light extraction surface 6 of thewavelength converting portion 4 that covers the light-emitting element 3can be reduced, and it is therefore possible to irradiate theirradiation surface with light of uniform color.

In order to evaluate the color nonuniformity of the light emitted fromthe produced light-emitting device 1, the color temperature of lightemitted with a forward current If =350 mA was measured. The measuringmethod will be described with reference to FIG. 7. FIG. 7 is a schematicdiagram used to illustrate a method for measuring the color temperatureof the light emitted from the light-emitting device. In the state wherethe light-emitting device 1 is caused to emit light, the colortemperature of emitted light that passes through a semicircle having aradius of 1 m (indicated by the dashed line in FIG. 7) from thelight-emitting device 1 serving as the center point was measured byusing a detector 59 (S9219 available from Hamamatsu Photonics K.K.,diameter of light-receiving surface: 11.3 mm). Then, radiation anglestheta relative to the optical axis L of the light-emitting element 3versus color temperature differences relative to a color temperature(about 3600 [K]) when theta =0 degrees were plotted. The obtained resultis shown in FIG. 8.

As can be seen from FIG. 8, according to the light-emitting device 1 ofthe present embodiment, the color temperature difference is reduced, andas a result, the color nonuniformity can be reduced.

In the present embodiment, the light-emitting element 3 is divided intotwo diodes: a diode in the edge portion and a diode in the inner regionlocated inside the edge portion, but the light-emitting element 3 may bedivided into three or more diodes. According to this configuration, theluminance of primary light emitted from each region of the lightextraction surface 5 of the light-emitting element 3 can be adjustedfinely, and it is therefore possible to irradiate the irradiationsurface with light of more uniform color. The area and current densityof the light-emitting layers of the diodes that are connected in seriesare substantially inversely proportional to each other, and thelight-emitting area and the luminance are also substantially inverselyproportional to each other. It is also possible to employ aconfiguration in which a plurality of diodes are connected in series, aplurality of which are connected in parallel.

Embodiment 2

A light-emitting device according to Embodiment 2 of the presentinvention will be described next with reference to FIG. 9. FIG. 9 showsdiagrams that more specifically show a light-emitting element that isused in the light-emitting device of the present embodiment. FIG. 9( a)is a cross-sectional view, and FIG. 9( b) is a plan view showing a sideopposite to the light extraction surface. The basic configuration of thelight-emitting device of the present embodiment is the same as that ofEmbodiment 1 described above (see FIGS. 1 to 3).

As shown in FIGS. 9( a) and 9(b), an n-GaN-based semiconductor layer 9,a light-emitting layer 10 and a p-GaN-based semiconductor layer 11 arelaminated in this order on one principal surface of a growth substrate 7made of GaN, SiC, sapphire or the like. The other principal surface ofthe growth substrate 7 is processed to have an uneven structure.

An isolation groove 20 for separating a light-emitting element 3 into aportion corresponding to the edge portion 5 a of the light extractionsurface 5 and a portion corresponding to the inner region 5 b locatedinside the edge portion 5 a is provided such that the isolation groove20 spans across the p-GaN-based semiconductor layer 11, thelight-emitting layer 10, and part of the n-GaN-based semiconductor layer9. Thereby, the light-emitting element 3 is divided into two diodes: adiode in the edge portion and a diode in the inner region located insidethe edge portion.

Rh/Pt/Au electrodes 13 a and 13 b that are highly reflective electrodesare provided as an anode electrode on the p-GaN-based semiconductorlayer 11 at the edge portion and the inner region located inside theedge portion, and the Rh/Pt/Au electrode 13 a of the edge portion andthe Rh/Pt/Au electrode 13 b of the inner region located inside the edgeportion are electrically connected to anode terminals 14 a and 14 b,respectively. A Ti/Au electrode 15 serving as a cathode electrode isprovided in the n-GaN-based semi-conductor layer 9 at the inner regionlocated inside the edge portion, and the Ti/Au electrode 15 iselectrically connected to a cathode terminal 16. An insulating layer 18made of silicon nitride is interposed inside the isolation groove 20,and between the anode terminals 14 a, 14 b and cathode terminal 16, andthe n-GaN-based semi-conductor layer 9, light-emitting layer 10 andp-GaN-based semiconductor layer 11.

The light-emitting element 3 of the present embodiment has theabove-described configuration, and the diode in the edge portion and thediode in the inner region located inside the edge portion are configuredsuch that they can be driven electrically independently of each other.

As described above, the light-emitting element 3 of the presentembodiment is divided into two diodes: a diode in the edge portion and adiode in the inner region located inside the edge portion, and the diodein the edge portion and the diode in the inner region located inside theedge portion are configured such that they can be driven electricallyindependently of each other. Therefore, a current can be injected suchthat the luminance of the primary light emitted from the edge portion 5a of the light extraction surface 5 of the light-emitting element 3 ishigher than the luminance of the primary light emitted from the innerregion 5 b located inside the edge portion 5 a. For example, as shown inFIG. 9( b), the diode D3 of the edge portion to which a variableresistor R1 is connected in series is connected in parallel with thediode D4 of the inner region located inside the edge portion to which avariable resistor R2 is connected in series, and by adjusting theresistance values of the variable resistors R1 and R2, a current can beinjected such that the luminance of the primary light emitted from theedge portion 5 a of the light extraction surface 5 is higher than theluminance of the primary light emitted from the inner region 5 b locatedinside the edge portion 5 a. With this configuration, balance adjustmentcan be performed by separately adjusting the amount of current injectedinto the diode in the edge portion and the amount of current injectedinto the diode in the inner region located inside the edge portion.

The current densities of the diodes D3 and D4 can be changed as well bychanging the resistance component of the light-emitting element 3,instead of changing the resistance values of the variable resistors R1and R2 provided outside the light-emitting element 3. For example, ifthe area of the light-emitting layer of each diode is changed, theinternal resistance value of the diode having a larger area decreasesrelatively, causing a large current to flow therethrough, and increasingthe current density. The internal resistance value can be changed alsoby other methods such as selecting materials for the wiring and theelectrodes of the light-emitting element 3 as appropriate, and changingthe doping amount doped into the semiconductor layer. By changing thecurrent density using the internal resistance value, the power sourceconfiguration of the light-emitting element 3 can be simplified.

Similarly to the case of Embodiment 1 described above, thelight-emitting element 3 of the present invention also is mounted on thebase 2, and is covered tightly with a wavelength converting portion 4 toform a light-emitting device (see FIG. 6). Because a configuration isadopted in which the luminance of the primary light emitted from theedge portion 5 a of the light extraction surface 5 of the light-emittingelement 3 is made higher than the luminance of the primary light emittedfrom the inner region 5 b located inside the edge portion 5 a asdescribed above, the light color difference across the light extractionsurface 6 (see FIG. 6) of the wavelength converting portion 4 thatcovers the light-emitting element 3 can be reduced, and it is thereforepossible to irradiate the irradiation surface with light of uniformcolor.

In the present embodiment, the light-emitting element 3 is divided intotwo diodes: a diode in the edge portion and a diode in the inner regionlocated inside the edge portion, but the light-emitting element 3 may bedivided into three or more diodes. According to this configuration, theluminance of primary light emitted from each region of the lightextraction surface 5 of the light-emitting element 3 can be adjustedfinely, and it is therefore possible to irradiate the irradiationsurface with light of more uniform color.

Embodiment 3

A light-emitting device according to Embodiment 3 of the presentinvention will be described next with reference to FIGS. 10 and 11. FIG.10 shows diagrams that more specifically show a light-emitting elementthat is used in the light-emitting device of the present embodiment.FIG. 10( a) is a cross-sectional view, and FIG. 10( b) is a plan viewshowing a light extraction surface. FIG. 11 is a cross-sectional viewthat more specifically shows the light-emitting device of the presentembodiment. The basic configuration of the light-emitting device of thepresent embodiment is the same as that of Embodiment 1 described above(see FIGS. 1 to 3).

As shown in FIGS. 10( a) and 10(b), a light-emitting element 3 of thepresent embodiment is formed on one principal surface of a base 21 madeof a conductive material such as GaN or SiC. A Rh/Pt/Au electrode 23which is a highly reflective electrode is provided as an anode electrodeon the principal surface of the base 21 with an Au/Sn adhesion layer 22interposed therebetween. On the Rh/Pt/Au electrode 23, a laminate inwhich a p-GaN-based semiconductor layer 11, a light-emitting layer 10and an n-GaN-based semiconductor layer 9 are laminated in this order isprovided. The light extraction surface 5 of the n-GaN-basedsemiconductor layer 9 is processed to have an uneven structure. Thereby,the light extraction efficiency of the light-emitting device can beimproved. An anode terminal 24 is provided on the other principalsurface of the base 21. A Ti/Au electrode 25 serving as a cathodeelectrode is provided only in the edge portion of the n-GaN-basedsemiconductor layer 9, and the Ti/Au electrode 25 is connectedelectrically to a cathode terminal 26. An insulating layer 28 made ofsilicon nitride is interposed between the cathode terminal 26 and then-GaN-based semiconductor layer 9, light-emitting layer 10, p-GaN-basedsemi-conductor layer 11 and base 21.

The growth substrate (not shown) of the light-emitting element 3 isremoved after it is bonded to the base 21 with a bonding material, suchas an Au/Sn adhesion layer 22, interposed therebetween, whereby thelight-emitting element 3 is obtained. The growth substrate can beremoved by the laser lift-off technique, polishing, etching technique orthe like, which are a common technique.

The light-emitting element 3 of the present embodiment has theabove-described configuration.

As described above, in the light-emitting element 3 of the presentembodiment, the Ti/Au electrode 25 serving as a cathode electrode isprovided only on the edge portion. Thereby, the current density of theedge portion can be increased, and it is therefore possible to make theluminance of the primary light emitted from the edge portion 5 a of thelight extraction surface 5 of the light-emitting element 3 higher thanthe luminance of the primary light emitted from the inner region 5 blocated inside the edge portion 5 a.

As shown in FIG. 11, the light-emitting element 3 formed on the base 21is covered tightly with the wavelength converting portion 4. In thepresent embodiment, the height of the light-emitting element 3 (theheight from the upper surface of the insulating layer 28) is about 3micrometer, and the height of the wavelength converting portion 4 (theheight from the upper surface of the cathode terminal 26) is about 0.1mm. Because a configuration is adopted in which the luminance of theprimary light emitted from the edge portion 5 a of the light extractionsurface 5 of the light-emitting element 3 is made higher than theluminance of the primary light emitted from the inner region 5 b locatedinside the edge portion 5 a as described above, the light colordifference across the light extraction surface 6 of the wavelengthconverting portion 4 that covers the light-emitting element 3 can bereduced, and it is therefore possible to irradiate the irradiationsurface with light of uniform color.

In the present embodiment, the cathode electrode is provided only on theedge portion, but the present invention is not necessarily limited tothis configuration, and it is sufficient that at least one of thecathode electrode and the anode electrode is provided only on the edgeportion.

Embodiment 4

A light-emitting device according to Embodiment 4 of the presentinvention will be described next with reference to FIGS. 12 and 13. FIG.12 shows diagrams that specifically show an example of a light-emittingelement that is used in a light-emitting device according to the presentembodiment. FIG. 12( a) is a cross-sectional view, and FIG. 12( b) is aplan view showing a light extraction surface. FIG. 13 shows diagramsthat specifically show another example of the light-emitting elementthat is used in the light-emitting device according to the presentembodiment. FIG. 13( a) is a cross-sectional view, and FIG. 13( b) is aplan view showing a light extraction surface. The basic configuration ofthe light-emitting device of the present embodiment is the same as thatof Embodiment 1 described above (see FIGS. 1 to 3).

The light-emitting element 3 of the present embodiment has the sameconfiguration as that of the light-emitting element 3 of Embodiment 3described above (see FIG. 10), except that the configuration of thecathode electrode is different. Accordingly, only the configuration ofthe cathode electrode will be described in the present embodiment.Furthermore, constituent members that are the same as those of thelight-emitting element 3 of Embodiment 3 described above are given thesame reference numerals, and descriptions thereof are omitted here.

As shown in FIGS. 12( a) and 12(b), a Ti/Au electrode 25 serving as acathode electrode is provided on the upper surface of an n-GaN-basedsemiconductor layer 9, and the Ti/Au electrode 25 is electricallyconnected to a cathode terminal 26.

The Ti/Au electrode 25 is provided in the form of a grid of squares overthe edge portion and the inner region located inside the edge portion.In this case, the electrode spacing L1 of the Ti/Au electrode 25 of theedge portion is smaller than the electrode spacing L2 of the Ti/Auelectrode 25 of the inner region located inside the edge portion.

The light-emitting element 3 of the present embodiment has theabove-described configuration.

As described above, in the light-emitting element 3 of the presentembodiment, for the Ti/Au electrode 25 serving as a cathode electrode,the electrode spacing L1 in the edge portion is made smaller than theelectrode spacing L2 in the inner region located inside the edgeportion, whereby the current density of the edge portion can beincreased, and it is therefore possible to make the luminance of theprimary light emitted from the edge portion 5 a of the light extractionsurface 5 of the light-emitting element 3 higher than the luminance ofthe primary light emitted from the inner region 5 b located inside theedge portion 5 a. As a result, similar to the case of Embodiment 3, thelight color difference across the light extraction surface 6 (see FIG.11) of the wavelength converting portion 4 that covers thelight-emitting element 3 can be reduced, and it is therefore possible toirradiate the irradiation surface with light of uniform color.

Also in the light-emitting element 3 shown in FIGS. 13( a) and 13(b), aTi/Au electrode 25 serving as a cathode electrode is provided on theupper surface of an n-GaN-based semiconductor layer 9, and the Ti/Auelectrode 25 is connected electrically to a cathode terminal 26.

The Ti/Au electrode 25 is provided in a hexagonal spider web-likepattern over the edge portion and the inner region located inside theedge portion. In this case, the electrode spacing L3 of the Ti/Auelectrode 25 of the edge portion is smaller than the electrode spacingL4 of the Ti/Au electrode 25 of the inner region located inside the edgeportion. Accordingly, similar to the above-described case, in this casealso, it is possible to irradiate the irradiation surface with light ofuniform color.

In the present embodiment, only for the cathode electrode, the electrodespacing in the edge portion is made smaller than the electrode spacingin the inner region located inside the edge portion, but the presentinvention is not necessarily limited to this configuration, and it issufficient that for at least one of the cathode electrode and the anodeelectrode, the electrode spacing in the edge portion is made smallerthan the electrode spacing in the inner region located inside the edgeportion.

Embodiment 5

A light-emitting device according to Embodiment 5 of the presentinvention will be described next with reference to FIG. 14. FIG. 14shows diagrams that specifically show an example of a light-emittingelement that is used in the light-emitting device of the presentembodiment. FIG. 14( a) is a cross-sectional view, and FIG. 14( b) is aplan view showing a light extraction surface. The basic configuration ofthe light-emitting device of the present embodiment is the same as thatof Embodiment 1 described above (see FIGS. 1 to 3).

A light-emitting element 3 of the present embodiment has the sameconfiguration as that of the light-emitting element 3 of Embodiment 3described above (see FIG. 10), except that the configuration of thecathode electrode is different. Accordingly, only the configuration ofthe cathode electrode will be described in the present embodiment.Furthermore, constituent members that are the same as those of thelight-emitting element 3 of Embodiment 3 described above are given thesame reference numerals, and descriptions thereof are omitted here.

As shown in FIGS. 14( a) and 14(b), on the upper surface of ann-GaN-based semi-conductor layer 9, an ITO electrode 29 that has aconcave-convex shape similar to the concave-convex shape of then-GaN-based semiconductor layer 9 and serves as a cathode electrode isprovided, and the ITO electrode 29 is electrically connected to acathode terminal 26.

The ITO electrode 29 is formed such that the edge portion has athickness greater than the thickness of the inner region located insidethe edge portion.

The light-emitting element 3 of the present embodiment has theabove-described configuration.

As described above, in the light-emitting element 3 of the presentembodiment, the ITO electrode 29 serving as a cathode electrode isformed such that the edge portion has a thickness greater than thethickness of the inner region located inside the edge portion, wherebythe electrode resistance of the edge portion of the ITO electrode 29 canbe made smaller than the electrode resistance of the inner regionlocated inside the edge portion. As a result, the current density of theedge portion can be increased, and thus the luminance of the primarylight emitted from the edge portion 5 a of the light extraction surface5 of the light-emitting device 3 can be made higher than the luminanceof the primary light emitted from the inner region 5 b located insidethe edge portion 5 a. With this, similar to the case of Embodiment 3,the light color difference across the light extraction surface 6 (seeFIG. 11) of the wavelength converting portion 4 that covers thelight-emitting element 3 can be reduced, and it is therefore possible toirradiate the irradiation surface with light of uniform color.

In the present embodiment, only for the cathode electrode, the electroderesistance of the edge portion is made smaller than the electroderesistance of the inner region located inside the edge portion, but thepresent invention is not necessarily limited to this configuration, andit is sufficient that for at least one of the cathode electrode and theanode electrode, the electrode resistance of the edge portion is madesmaller than the electrode resistance of the inner region located insidethe edge portion.

Embodiment 6

A light-emitting device according to Embodiment 6 of the presentinvention will be described next with reference to FIG. 15. FIG. 15shows diagrams that specifically show a light-emitting element that isused in the light-emitting device of the present embodiment. FIG. 15( a)is a cross-sectional view, and FIG. 15( b) is a plan view showing alight extraction surface. The basic configuration of the light-emittingdevice of the present embodiment is the same as that of Embodiment 1described above (see FIGS. 1 to 3).

As shown in FIGS. 15( a) and 15(b), a light-emitting element 3 of thepresent embodiment is formed on one principal surface of a base 30 madeof sapphire. An anode terminal 24 is provided on the principal surfaceof the base 30. A Rh/Pt/Au electrode 23, which is a highly reflectiveelectrode, is provided as an anode electrode on the anode terminal 24with an Au/Sn adhesion layer 22 interposed therebetween. On the Rh/Pt/Auelectrode 23, a laminate in which a p-GaN-based semiconductor layer 11,a light-emitting layer 10 and an n-GaN-based semiconductor layer 9 arelaminated in this order is provided. The light extraction surface 5 ofthe n-GaN-based semiconductor layer 9 is processed to have an unevenstructure.

A Ti/Au electrode 25 serving as a cathode electrode is provided only inthe edge portion of the n-GaN-based semiconductor layer 9, and the Ti/Auelectrode 25 is connected electrically to a cathode terminal 26. Aninsulating layer 28 made of silicon nitride is interposed between thecathode terminal 26 and the n-GaN-based semi-conductor layer 9,light-emitting layer 10, p-GaN-based semiconductor layer 11 and anodeterminal 24.

In the n-GaN-based semiconductor layer 9 or the p-GaN-basedsemiconductor layer 11 of the light-emitting element 3, the inner regionlocated inside the edge portion is formed into a high resistance regionby, for example, Zn ion implantation, and the edge portion is formedinto a low resistance region by doping the edge portion with a dopantagent at a high concentration, for example, in the case of then-GaN-based semi-conductor layer, it is doped with Si, and in the caseof the p-GaN-based semiconductor layer, it is doped with Mg. In otherwords, in the light-emitting element 3, the internal resistance of theinner region located inside the edge portion is greater than theinternal resistance of the edge portion.

The light-emitting element 3 of the present embodiment has theabove-described configuration.

As described above, in the light-emitting element 3 of the presentembodiment, the internal resistance of the inner region located insidethe edge portion is made greater than the internal resistance of theedge portion, whereby the current density of the edge portion can beincreased, and it is therefore possible to make the luminance of theprimary light emitted from the edge portion 5 a of the light extractionsurface 5 of the light-emitting element 3 higher than the luminance ofthe primary light emitted from the inner region 5 b located inside theedge portion 5 a. As a result, similar to the case of Embodiment 3described above, the light color difference across the light extractionsurface 6 (see FIG. 11) of the wavelength converting portion 4 thatcovers the light-emitting element 3 can be reduced, and it is thereforepossible to irradiate the irradiation surface with light of uniformcolor.

In the present embodiment, methods such as ion implantation and highconcentration doping are employed to make the internal resistance of theinner region located inside the edge portion greater than the internalresistance of the edge portion, but the present invention is not limitedto these methods.

Embodiment 7

A light-emitting device according to Embodiment 6 of the presentinvention will be described next with reference to FIGS. 16 and 17. FIG.16 shows diagrams that specifically show an example of a light-emittingelement that is used in the light-emitting device of the presentembodiment. FIG. 16( a) is a cross-sectional view, and FIG. 16( b) is aplan view showing a light extraction surface. FIG. 17 shows diagramsthat specifically show another example of the light-emitting elementthat is used in the light-emitting device of the present embodiment.FIG. 17( a) is a cross-sectional view, and FIG. 17( b) is a plan viewshowing a light extraction surface. The basic configuration of thelight-emitting device of the present embodiment is the same as that ofEmbodiment 1 described above (see FIGS. 1 to 3).

The light-emitting element 3 of the present embodiment has the sameconfiguration as that of the light-emitting element 3 of Embodiment 3described above (see FIG. 10), except that only the configuration of then-GaN-based semiconductor layer and the cathode electrode, or theconfiguration of the n-GaN-based semiconductor layer is different.Accordingly, only the configuration of the n-GaN-based semiconductorlayer and the cathode electrode, or the configuration of the n-GaN-basedsemiconductor layer will be described in the present embodiment.Furthermore, constituent members that are the same as those of thelight-emitting element 3 of Embodiment 3 described above are given thesame reference numerals, and descriptions thereof are omitted here.

As shown in FIGS. 16( a) and 16(b), the light extraction surface 5 of ann-GaN-based semiconductor layer 31 is processed to be flat, and a flatplate-like cathode electrode 32 is provided on the upper surface of then-GaN-based semiconductor layer 31. The cathode electrode 32 isconnected electrically to a cathode terminal 26.

The edge portion of the cathode electrode 32 is configured of adielectric multilayer film in which thin films made of metal oxides suchas SiO₂, ZnO, TiO₂, Ta₂O₃, Nb₂O₅ and ZnS are periodically laminated.Accordingly, the edge portion of the cathode electrode 32 is a hightransmissivity region. In other words, in the light-emitting element 3,the transmissivity of the primary light emitted from the edge portion isgreater than the transmissivity of the primary light emitted from theinner region located inside the edge portion.

The light-emitting element 3 of the present embodiment has theabove-described configuration.

As described above, in the light-emitting element 3 of the presentembodiment, the transmissivity of the primary light emitted from theedge portion is made higher than the transmissivity of the primary lightemitted from the inner region located inside the edge portion, wherebythe luminance of the primary light emitted from the edge portion 5 a ofthe light extraction surface 5 of the light-emitting element 3 can bemade higher than the luminance of the primary light emitted from theinner region 5 b located inside the edge portion 5 a. As a result,similar to the case of Embodiment 3, the light color difference acrossthe light extraction surface 6 (see FIG. 11) of the wavelengthconverting portion 4 that covers the light-emitting element 3 can bereduced, and it is therefore possible to irradiate the irradiationsurface with light of uniform color.

In a light-emitting element 3 shown in FIGS. 17( a) and 17(b), only theedge portion of the light extraction surface 5 of an n-GaN-basedsemiconductor layer 33 is processed to have an uneven structure.Accordingly, the edge portion of the n-GaN-based semiconductor layer 33is a high transmissivity region. Therefore, similar to the above, theluminance of the primary light emitted from the edge portion 5 a of thelight extraction surface 5 of the light-emitting element 3 can be madehigher than the luminance of the primary light emitted from the innerregion 5 b located inside the edge portion 5 a.

Embodiment 8

A light-emitting device according to Embodiment 8 of the presentinvention will be described next with reference to FIG. 18. FIG. 18 is aschematic cross-sectional view showing an example of a light-emittingdevice according to Embodiment 8 of the present invention.

As shown in FIG. 18, a light-emitting device 34 of the presentembodiment includes a base 35 having a recess, and a singlelight-emitting element 36 that is disposed at the bottom of the recess(on the base 35). In the present embodiment, the bottom and inner wallsurface of the recess are light reflecting, so that light (primarylight) emitted from the light-emitting element 36 can be reflectedtoward the opening of the recess. The inner wall surface of the recessis flared toward the opening of the recess. This improves the lightextraction efficiency of the light-emitting device 34.

There is no particular limitation on the material for constituting thebase 35, and it is possible to use, for example, monocrystals such assapphire Si, GaN, AlN, ZnO, SiC, BN and ZnS; ceramics such as Al₂O₃,AlN, BN, MgO, ZnO, SiC and C, and mixtures thereof; metals such as Al,Cu, Fe, Au and W, and alloys that include these metals; glass epoxy;resins such as epoxy resin, silicone resin, acrylic resin, urea resin,amide resin, imide resin, polycarbonate resin, polyphenyl sulfide resin,liquid crystal polymer, acrylonitrile-butadiene-styrene resin (ABSresin), methacrylate resin (PMMA resin) and cyclic olefin copolymer, andmixtures thereof.

Also, there is no particular limitation on the configuration andmounting method of the light-emitting element 36. Examples of theconfiguration of the base include a lead frame base, a package base inwhich a light-emitting element is mounted, and a submount base that isinterposed between a light-emitting element and a package base.

The light-emitting element 36 is a light-emitting element that emitslight that is absorbed by a wavelength converting material. As thelight-emitting element, it is possible to use, for example, a green LEDthat emits green light having a wavelength of 500 to 550 nm, a blue LEDthat emits blue light having a wavelength of 420 to 500 nm, ablue-violet LED that emits blue-violet light having a wavelength of 380to 420 nm, and an ultraviolet LED having an even shorter wavelength. Inthe case of a nitride semiconductor material, it is represented by ageneral formula: B_(z)Al_(x)Ga_(1-x-y-z)In_(y)N (where x is in the rangeof 0 to 1, y is in the range of 0 to 1, z is in the range of 0 to 1, andx+y+z is in the range of 0 to 1). Hereinafter, this is referred to as“GaN-based semiconductor”. It is also possible to use a II-VI groupsemiconductor material such as ZnS or ZnO.

The light-emitting element is not limited to those made of a compoundsemi-conductor material, and it is also possible to use light-emittingelements made of an organic semiconductor material or an inorganicsemiconductor material.

As the method for mounting the light-emitting element 36, for example, amethod as shown in enlarged cross-sectional views of FIGS. 19( a) to19(c) can be used.

In the example shown in FIG. 19( a), a Ni/Au electrode 45 that serves asan anode electrode provided on a p-GaN-based semiconductor layer 36 awhich is a p-type semi-conductor layer is wire-bonded to metal wiring 42formed on a base 35 by an Au wire 48. In the example shown in FIG. 19(a), an n-SiC substrate 36 d can be used as the substrate of thelight-emitting element 36, and an n-GaN layer 36 c that is disposed onthe n-SiC substrate 36 d and serves as an n-type semiconductor layer iselectrically connected to a Ni/Ag/Pt/Au electrode 49 serving as acathode electrode with the n-SiC substrate 36 d interposed therebetween.In other words, the n-SiC substrate 36 d is connected electrically tothe metal wiring 42 via the Ni/Ag/Pt/Au electrode 49 which is a highlyreflective electrode. In FIG. 19( a), reference numeral 36 b denotes alight-emitting layer.

In the example shown in FIG. 19( b), the light-emitting element 36 isconfigured by sequentially laminating, from the side of the metal wiring42, a p-GaN-based semi-conductor layer 36 a as a p-type semiconductorlayer, a GaN-based semiconductor light-emitting layer 36 b, ann-GaN-based semiconductor layer 36 c as an n-type semi-conducator layer,and a sapphire substrate 36 e. A Rh/Pt/Au electrode 44, which is ahighly reflective electrode, is provided as an anode electrode on thep-GaN-based semiconductor layer 36 a, and the Rh/Pt/Au electrode 44 isbonded to bumps 43. A Ni/Au electrode 45 is provided as a cathodeelectrode on a portion of the n-GaN-based semiconductor layer 36 c, andthe Ni/Au electrode 45 also is bonded to a bump 43. Thereby, thelight-emitting element 36 is flip-chip mounted onto the metal wiring 42formed on the base 35 with the bumps 43 therebetween.

In the example shown in FIG. 19( c), the light-emitting element 36 ismounted on the base 35 by attaching the Rh/Pt/Au terminal 44 serving asan anode electrode to the base 35 with an Au/Sn adhesion layer 55. TheAu/Sn adhesion layer 55 is connected electrically to a Ti/Pt/Auelectrode 50 disposed on the base 35. The n-GaN layer 36 c is connectedelectrically to a metal wiring 51 formed on the base 35 with a Ti/Auelectrode 46 serving as a cathode electrode interposed therebetween. Asurface of the n-GaN layer 36 c is processed to have an unevenstructure. Thereby, the light extraction efficiency of thelight-emitting device 34 can be improved. A silicon nitride film 47serving as an insulating layer is interposed between the side face ofthe light-emitting element 3 and the Ti/Au electrode 46.

As shown in FIG. 18, in the light-emitting device 34 of the presentembodiment, the light-emitting element 36 is covered tightly with afirst cover portion 37, and the side face of the first cover portion 37is surrounded tightly by a second cover portion 38. Here, the first andsecond cover portions 37 and 38 are formed such that their uppersurfaces are flush with each other. Furthermore, the first and secondcover portions 37 and 38 are covered tightly with a plate-likewavelength converting portion 39. The wavelength converting portion 39has a uniform thickness, and a wavelength converting materialconstituting the wavelength converting portion 39 is distributeduniformly. The upper surface of the wavelength converting portion 39 isflush with the surface of the base 35 in which there is an opening ofthe recess. And, light (primary light) emitted from the light-emittingelement and secondary light obtained through absorption and conversionof the primary light by the wavelength converting material are mixed inthe wavelength converting portion 39, and this mixed light is emittedfrom the upper surface of the wavelength converting portion 39.

The refractive index of the second cover portion 38 is set higher thanthe refractive index of the first cover portion 37. In other words, inthe light-emitting device 34 of the present embodiment, the coverportion (the second cover portion 38) in the outer periphery of thewavelength converting portion 39 has a refractive index higher than thatof the other portion of the cover portion (the first cover portion 37).As the distance from the light-emitting element 36 to the interfacebetween the first cover portion 37 and the second cover portion 38becomes shorter, the effect of the present invention to achieve a thinlight-emitting device with less color nonuniformity can be attained byshortening the distance between the light-emitting element and thewavelength converting portion. As the yardstick, it is sufficient tomake the distance between the interface between the first cover portion37 and the second cover portion 38 and the periphery of thelight-emitting element 36 smaller than the distance between thelight-emitting element 36 and the wavelength converting portion 39. Itis preferable that the distance between the interface between the firstcover portion 37 and the second cover portion 38 and the periphery ofthe light-emitting element 36 is 1 mm or less, preferably 0.5 mm orless, and more preferably 0.2 mm or less. As will be described later,the interface may be in contact with the light-emitting element.

According to the light-emitting device 34 of the present embodiment, therefractive index (n₂) of the cover portion (the second cover portion 38)in the outer periphery of the wavelength converting portion 39 is sethigher than the refractive index (n₁) of the other portion (the firstcover portion 37) of the cover portion, whereby light (primary light)emitted from the light-emitting element 36 can be caused to enteruniformly the wavelength converting portion 39. Particularly when therefractive index ratio (n₁/n₂) is 0.9 or less, light (primary light)emitted from the light-emitting element 36 can be caused to entersufficiently uniformly the wavelength converting portion 39.

Ordinarily, the light intensity of light (primary light) emitted from alight-emitting element is high in the substantially vertically upwarddirection, and is smaller as it moves in the lateral direction. However,according to the configuration of the light-emitting device 34 of thepresent embodiment, as described in the foregoing, light (primary light)emitted from the light-emitting element 36 can be caused to enter thewavelength converting portion 39 uniformly, and thus the primary lightcan be caused to enter the wavelength converting portion 39 having auniform thickness and a uniform distribution of a wavelength convertingmaterial at a uniform intensity from the undersurface of the wavelengthconverting portion 39. Consequently, uniformly mixed light can beemitted from the upper surface of the wavelength converting portion 39,and it is therefore possible to reduce the color nonuniformity of lightextracted from the light-emitting device 34. In other words, thelight-emitting device 34 of the present embodiment includes a primarylight intensity distribution control means for setting the intensitydistribution of the primary light within the wavelength convertingportion 39 such that the mixing ratio of the primary light and thesecondary light that are emitted from the light extraction surface ofthe wavelength converting portion 39 is substantially uniform.

By adopting a configuration as that of the light-emitting device 34 ofthe present embodiment, primary light can be caused to enter at auniform intensity from the undersurface of the wavelength convertingportion without increasing the distance between the light-emittingelement and the wavelength converting portion, and thus even in a thinLED, uniformly mixed light can be emitted from the upper surface of thewavelength converting portion.

In order to control the refractive indexes of the first and second coverportions 37 and 38 as described above, for example, it is sufficient toselect materials constituting the first and second cover portions 37 and38 such that the refractive indexes of the cover portions 37 and 38satisfy the above-described relationship.

There is no particular limitation on the materials constituting thefirst and second cover portions 37 and 38. Various materials can be usedas long as at least part of the light emitted from the light-emittingelement 3 can pass through the first and second cover portions 37 and38. For example, it is possible to use metal oxides such as aluminumoxide (refractive index: 1.63), cerium oxide (refractive index: 2.2),hafnium oxide (refractive index: 1.95), magnesium oxide (refractiveindex: 1.74), niobium oxide (refractive index: 2.33), tantalum oxide(refractive index: 2.16), zirconium oxide (refractive index: 2.05), zincoxide (refractive index: 2.1), titanium oxide (refractive index: 2.4),yttrium oxide (refractive index: 1.87), silicon oxide (refractive index:1.5), indium oxide (refractive index: 2), tin oxide (refractive index:2), tungsten oxide (refractive index: 2.2) and vanadium oxide(refractive index: 2.0); inorganic materials such as silicon nitride(refractive index: 1.9), gallium nitride (refractive index: 2.5),silicon carbide (refractive index: 2.6), calcium fluoride (refractiveindex: 1.43), calcium carbonate (refractive index: 1.58), barium sulfate(refractive index: 1.64), copper sulfide (refractive index: 2.1), tinsulfide (refractive index: 2.0) and zinc sulfide (refractive index:2.37); diamond (refractive index: 2.4); and mixtures thereof. Therefractive index values within parentheses indicate the refractive indexof the respective materials with respect to light having a wavelength of550 nm.

As the method for forming the first and second cover portions 37 and 38using the above-listed materials, for example, sol-gel method can beused. For example, when forming a cover portion made of silicon oxide bysol-gel method, metal alkoxide (methylsilicate, N-butyl silicate, etc.)is hydrolyzed to form a sol. After that, the viscosity of the resultingsol is adjusted to a predetermined value using an alcohol such asethylene glycol. The resultant is applied onto desired locations on abase, dried at 200 degrees C. for several tens of minutes, and thenheated at 300 degrees C. for about two hours. Thereby, a cover portionmade of silicon oxide is obtained. When forming a cover portion using ametal oxide other than silicon oxide such as titanium oxide, the samemethod can be used. When forming a cover portion by sol-gel method, ananoparticle material described later can be used in combination. Forexample, a nanoparticle material is dispersed in a metal alkoxide toform a gel, whereby a cover portion made of a metal oxide and ananoparticle material is obtained. As a method for adjusting therefractive index, by adopting a method in which the mixing ratio of atleast two of the above-listed materials having different refractiveindexes is changed, adjustment can be effected between the refractiveindexes of the materials. In other words, the refractive index of thecover portion can be increased by selecting a material having a highrefractive index, or increasing the mixing ratio of the material.

As the materials constituting the first and second cover portions 37 and38, resins such as epoxy resin, silicone resin, acrylic resin, urearesin, amide resin, imide resin, polycarbonate resin, polyphenyl sulfideresin, liquid crystal polymer, ABS resin, PMMA resin and cyclic olefincopolymer; resins made of a mixture thereof; or glass such as lowmelting point glass may be used. When using a light-transmittingmaterial such as these resins or glass, the refractive index of thelight-transmitting material can be increased by irradiating an electronbeam or ion beam (hydrogen ion beam, helium ion beam or the like) to thelight-transmitting material. It is also possible to use a compositematerial obtained by dispersing a nanoparticle material made of a metaloxide or inorganic material listed above in the light-transmittingmaterial serving as a base material. In this case, the refractive indexof the cover portion can be adjusted by adjusting the amount of thenanoparticle material that is dispersed in the base material. When acurable resin is used as the base material, the thixotropy of thecurable resin before being cured can be improved by dispersing thenanoparticle material in the curable resin in an uncured state, so thatthe cover portion can be easily formed into a desired shape.Furthermore, because the heat conductivity is improved as compared tothe case of using a resin alone, heat from the light-emitting element 3can be dissipated with high efficiency.

As the materials constituting the first and second cover portions 37 and38, a composite material obtained by dispersing a nanoparticle materialin the light-transmitting material serving as a base material may beused. As the nanoparticle material, for example, ultrafine particlesmade of a metal oxide, inorganic material listed above or the like canbe used, and it is preferable to use ultrafine particles having anaverage particle size equal to or less than one forth of the luminouswavelength within the light-transmitting material which is a materialconstituting the cover portion. This is because a cover portion havingsufficient transparency can be obtained as long as the nanoparticlematerial has an average particle size within that range. “Averageparticle size” used above may be an average value (e.g., the averagevalue of the particle sizes of 100 primary particles) of the particlesizes of primary particles that are observed from an image obtained by ascanning electron microscope. Particularly, it is sufficient that theaverage particle size is 1 nm or more and 100 nm or less, preferably 1nm or more and 50 nm or less. From the viewpoint of dispersibility, 1 nmor more and 10 nm or less is more preferable. As a method for adjustingthe refractive index, by adopting a method in which the mixing ratio ofthe light-transmitting material serving as a base material and ananoparticle material as described above having a refractive indexdifferent from that of the base material is changed, adjustment can beeffected between the refractive indexes of the materials. In otherwords, the refractive index of the cover portion can be increased byselecting a material having a high refractive index, or increasing themixing ratio of the material.

The wavelength converting portion 6 is made of, for example, awavelength converting material and a light-transmitting material servingas a base material for dispersing the wavelength converting material.

As the wavelength converting material, for example, a fluorescentmaterial can be used. As the fluorescent material, it is possible touse, for example, a red fluorescent material that emits red light, anorange fluorescent material that emits orange light, a yellowfluorescent material that emits yellow light, a green fluorescentmaterial that emits green light, and so on. As the red fluorescentmaterial, it is possible to use, for example, silicate-based materialsuch as Ba₃MgSi₂O₈:Eu²⁺, Mn²⁺, a nitridosilicate-based material such asSr₂Si₅N₈:Eu²⁺, a nitridoaluminosilicate-based material such asCaAlSiN₃:Eu²⁺, an oxonitridoaluminosilicate-based material such asSr₂Si₄AlON₇:Eu²⁺, a sulfide-based material such as (Sr, Ca)S:Eu²⁺,La₂O₂S:Eu³⁺, and so on. As the orange fluorescent material, it ispossible to use, for example, a silicate-based material such as (Sr,Ca)₂SiO₄:Eu²⁺, a garnet-based material such as Gd₃Al₅O₁₂:Ce³⁺, aCa-alpha-sialon-based material such as Ca-alpha-SiAlON:Eu²⁺, and so on.As the yellow fluorescent material, it is possible to use, for example,a silicate-based material such as (Sr, Ca)₂SiO₄:Eu²⁺, a garnet-basedmaterial such as (Y,Gd)₃Al₅O₁₂:Ce³⁺, a sulfide-based material such asCaGa₂S₄:Eu²⁺, a Ca-alpha-sialon-based material such asCa-alpha-SiAlON:Eu²⁺, and so on. As the green fluorescent material, itis possible to use, for example, an aluminate-based material such asBaMgAl₁₀O₁₇:Eu²⁺, Mn²⁺ or (Ba, Sr, Ca)Al₂O₄:Eu²⁺, a silicate-basedmaterial such as (Ba, Sr)₂SiO₄:Eu²⁺, a Ca-alpha-sialon-based materialsuch as Ca-alpha-SiAlON:Yb²⁺, a beta-sialon-based material such asbeta-Si₃N₄:Eu²⁺, an oxonitridoaluminosilicate-based material such as(Ba, Sr, Ca)₂Si₄AlON₇:Ce³⁺, a sulfide-based material such asSrGa₂S₄:Eu²⁺, a garnet-based material such as Y₃(Al,Ga)₅O₁₂:Ce³⁺, Y₃A1₅O₁₂:Ce³⁺, Ca₃Sr₂Si₃O₁₂:Ce³⁺ or BaY₂ SiAl₄O₁₂:Ce³⁺, an oxide-basedmaterial such as CaSc₂O₄:Ce³⁺, and so on. The light emitted from theupper surface of the wavelength converting portion is not limited towhite light, and fine light color designs are possible by selectingthese fluorescent materials as appropriate. And infinite variations arepossible by using a plurality of different types of fluorescentmaterials having different luminous wavelengths. Besides theconfiguration in which the wavelength converting material is disperseduniformly in the wavelength converting portion, the wavelengthconverting portion can have, for example, a configuration in which theconcentration of the wavelength converting material is changed from theundersurface of the wavelength converting portion substantiallygradually toward the upper surface thereof, a configuration in whichlayers made of different wavelength converting materials are laminated,a configuration in which cells made of different wavelength convertingmaterials are arranged in a matrix form, or the like. With any of theabove-described configurations, uniformly mixed light can be emittedfrom the upper surface of the wavelength converting portion by causingprimary light to enter from the undersurface of the wavelengthconverting portion at a uniform intensity.

As the light-transmitting material, any material can be used as long asit allows the light extracted from the light-emitting device 1 to passtherethrough. Examples thereof include resins such as epoxy resin,silicone resin, acrylic resin, urea resin, amide resin, imide resin,polycarbonate resin, polyphenyl sulfide resin, liquid crystal polymer,ABS resin, PMMA resin and cyclic olefin copolymer; resins made of amixture thereof; and glass such as low melting point glass. It is alsopossible to use a composite material obtained by dispersing metal oxideparticles in the light-transmitting material serving as a base material.In this case, the refractive index of the wavelength converting portion6 can be adjusted by adjusting the amount of the metal oxide particlesthat are dispersed in the base material. When a curable resin is used asthe base material, the thixotropy of the curable resin before beingcured can be improved by dispersing the metal oxide particles in thecurable resin in an uncured state, so that the wavelength convertingportion 6 can be easily formed into a desired shape. Furthermore,because the heat conductivity is improved as compared to the case ofusing a resin alone, heat from the light-emitting element 3 can bedissipated with high efficiency.

When a blue-violet LED or ultraviolet LED is used as the light-emittingelement 3, for example, the above-described fluorescent material may beused in combination with a blue fluorescent material that emits bluelight or a blue-green fluorescent material that emits blue-green light.As the blue fluorescent material, it is possible to use, for example, analuminate-based material such as BaMgAl₁₀O₁₇:Eu²⁺, a silicate-basedmaterial such as Ba₃MgSi₂O₈:Eu²⁺, a halophosphate-based material such as(Sr, Br)₁₀(PO₄)₆Cl₂:Eu²⁺, and so on. As the blue-green fluorescentmaterial, it is possible to use, for example, an aluminate-basedmaterial such as Sr₄Al₁₄O₂₅:Eu²⁺, a silicate-based material such asSr₂Si₃O₈-2SrCl₂:Eu²⁺, and so on.

In the light-emitting device 1 of the present embodiment, it ispreferable that a portion of the wavelength converting portion 6 that islocated above the portion of the cover portion having a high refractiveindex (the second cover portion 38) has a refractive index higher thanthat of the other portion of the wavelength converting portion 39 (theborder between the regions having different refractive indexes isindicated by dashed lines in FIG. 18). To control the refractive indexof the wavelength converting portion 39 as described above, for example,the amount of metal oxide particles that are dispersed in alight-transmitting material (base material) may be adjusted in themanner described above. According to this preferred configuration,reflection at the interface between the cover portion (the first andsecond cover portions 37 and 38) and the wavelength converting portion39 can be reduced, and thus a loss caused by the reflection can bereduced. Furthermore, in the wavelength converting portion 39, theintensity distribution can be made uniform.

The present embodiment has been described in the context of the basebeing a base 35 having a recess, but the present invention is notnecessarily limited to the use of a base having this configuration, andit is also possible to use, for example, a flat plate-like base similarto those used in Embodiments 10 and 11 described later.

Furthermore, the present embodiment has been described in the context ofthe first and second cover portions 37 and 38 being covered tightly withthe wavelength converting portion 39, but it is also possible to providea space 40 between the first and second cover portions 37 and 38 and thewavelength converting portion 39 as shown in FIG. 20. According to thisconfiguration, it is possible to suppress an increase in the temperatureof the wavelength converting portion 39 caused by heat from thelight-emitting element 36.

Furthermore, the present embodiment has been described in the context ofa single light-emitting element 36 being disposed on the base 35, butthe number of the light-emitting elements is not limited to a particularnumber, and it is possible to employ, for example, a configuration inwhich three light-emitting elements 36 f, 36 g and 36 h are disposed onthe base 35 as shown in FIG. 21. According to this configuration, theintensity of emitted light can be improved. It is also possible toemploy, for example, a configuration as shown in FIG. 22, in which twolight-emitting elements 36 f and 36 h are disposed on the base 35 and acover portion having a high refractive index (second cover portion 38)is disposed between the light-emitting elements 36 f and 36 h. When thespacing between the light-emitting elements is relatively large, thedistribution of primary light can be made uniform, and thus a thinsurface light source can be realized. This effect is effective also whenonly primary light is used without using the wavelength convertingportion. In this case, the light emitted from the light-emittingelements may be any of ultraviolet light, visible light and infraredlight.

In order to simplify the description, the present embodiment has beendescribed in the context of using two cover portions having differentrefractive indexes, but it is also possible to sequentially disposethree or more cover portions having different refractive indexes suchthat their refractive indexes are changed gradually.

EXAMPLE

Hereinafter, examples of the present invention will be described.However, it should be noted that the present invention is not limited tothe examples given below.

(Production of Light-Emitting Device)

As an example of the present invention, a light-emitting device shown inFIG. 23 was produced. As a comparative example, a light-emitting devicein which a single type of resin was used for the cover portion was alsoproduced (this light-emitting device had the same configuration as thatof the light-emitting device shown in FIG. 23 except for the material ofthe cover portion).

As a light-emitting element 36, an LED chip (thickness: 0.2 mm, 1.0 mmsquare) that emits light having a wavelength of about 460 nm was used.As a base 35 having a recess, a substrate made of ceramic Al₂O₃ wasused. The above LED chip was flip-chip mounted onto the bottom of therecess of the base 35 with Au bumps. The recess had a depth of 0.5 mm,and the upper opening of the recess had a diameter of 2 mm. As thematerial constituting a first cover portion 37, silicone resin having arefractive index of 1.5 with respective to light having a wavelength of550 nm was used. As the material constituting a second cover portion 38,a composite material obtained by dispersing titanium oxide particleshaving an average particle size of 5 nm and a refractive index of 2.0with respect to light having a wavelength of 550 nm in a silicone resinwas used. The distance between the interface between the first coverportion 37 and the second cover portion 38 and the periphery of thelight-emitting element 36 was about 0.2 mm. As the wavelength convertingmaterial for a wavelength converting portion 39, Y₃Al₅O₁₂:Ce³⁺ was used,and as the light-transmitting material serving as a base material forthe wavelength converting portion 39, a silicone resin was used. Thewavelength converting portion 39 had a thickness of about 0.05 mm.

(Method for Measuring Color Temperature of Emitted Light)

In order to evaluate the color nonuniformity of light emitted from theproduced light-emitting devices, the color temperature of the emittedlight was measured. The measuring method will be described withreference to FIG. 7. In the state where the light-emitting device 34 iscaused to emit light, the correlated color temperature of emitted lightthat passes through a semicircle having a radius of 1 m (indicated bythe dashed line in FIG. 24) from the light-emitting device 34 serving asthe center point was measured by using a detector 59 (S9219 availablefrom Hamamatsu Photonics K.K., diameter of light-receiving surface: 11.3mm). Then, radiation angles theta relative to the optical axis L of thelight-emitting element 36 versus correlated color temperaturedifferences relative to a correlated color temperature (about 6500 [K])when theta =0 degrees were plotted. The obtained result is shown in FIG.24. In FIG. 24, the result of the light-emitting device of thecomparative example measured in the same manner as above is shown aswell. It is preferable that the correlated color temperature differenceof the emitted light within the radiation angle used is within 200 [K].In the comparative example, the correlated color temperature differencewithin a radiation angle of plus or minus 70 [degrees] is about 230 [K],whereas in the present example, the correlated color temperaturedifference within a radiation angle of plus or minus 70 [degrees] is 120[K] which is within the target value, namely, 200 [K].

As can be seen from FIG. 24, according to the light-emitting device 34of the present example, the correlated color temperature difference issmall, so that the color unevenness can be reduced.

Embodiment 9

A light-emitting device according to Embodiment 9 of the presentinvention will be described next with reference to FIG. 25. FIG. 25 is across-sectional view showing an example of the light-emitting deviceaccording to Embodiment 9 of the present invention.

As shown in FIG. 25, a light-emitting device 52 of the presentembodiment includes a base 35 having a recess, and a singlelight-emitting element 36 that is disposed at the bottom of the recess(on the base 35). The light-emitting element 36 is covered with a firstcover portion 37 a in a tight contact state, and the upper outerperiphery of the first cover portion 37 a is replaced by a second coverportion 38 a. Here, the first and second cover portions 37 a and 38 aare formed such that their upper surfaces are flush with each other.Furthermore, the first and second cover portions 37 a and 38 a arecovered with a plate-like wavelength converting portion 39 in a tightcontact state. The wavelength converting portion 39 has a uniformthickness, and a wavelength converting material constituting thewavelength converting portion 39 is distributed uniformly. The uppersurface of the wavelength converting portion 39 is flush with thesurface of the base 35 in which there is an opening of the recess.

The refractive index of the second cover portion 38 a is set higher thanthe refractive index of the first cover portion 37 a. In other words, inthe light-emitting device 52 of the present embodiment, an upper portion(the second cover portion 38 a), that is, at least a portion of thecover portion, in the outer periphery of the wavelength convertingportion 39 has a refractive index higher than that of the other portionof the cover portion (the first cover portion 37 a). By shortening thedistance from the light-emitting element 36 to the interface between thefirst cover portion 37 a and the second cover portion 38 a, that is, byshortening the distance between the light-emitting element and thewavelength converting portion, the effect of the present invention toachieve a thin light-emitting device with less color nonuniformity canbe attained. As the yardstick, it is sufficient to make the distancebetween the interface between the first cover portion 37 a and thesecond cover portion 38 a and the periphery of the light-emittingelement smaller than the distance between the upper surface of thelight-emitting element 36 and the undersurface of the wavelengthconverting portion 39. The distance between the interface between thefirst cover portion 37 a and the second cover portion 38 a and theperiphery of the light-emitting element is 1 mm or less, preferably 0.5mm or less, and more preferably 0.2 mm or less. As will be describedlater, the interface may be in contact with the light-emitting element.

The configuration of the light-emitting device 52 of the presentembodiment also can provide effects similar to those obtained in thecase of the light-emitting device 34 of Embodiment 8 described above.

Other configurations, such as the configuration and mounting method ofthe light-emitting element 36 and the material of each member, are thesame as those of the light-emitting device 34 of Embodiment 8 describedabove.

Also in the light-emitting device 52 of the present embodiment, it ispreferable that a portion of the wavelength converting portion 39 thatis located above the portion of the cover portion having a highrefractive index (the second cover portion 38 a) has a refractive indexhigher than that of the other portion of the wavelength convertingportion 39 (the border between the regions having different refractiveindexes is indicated by dashed lines in FIG. 25).

Furthermore, as the base, a flat plate-like base similar to those usedin Embodiments 10 and 11 described later can be used in the presentembodiment.

The present embodiment also has been described in the context of thefirst and second cover portions 37 a and 38 a being covered tightly withthe wavelength converting portion 39, but it is also possible to providea space 40 between the first and second cover portions 37 a and 38 a andthe wavelength converting portion 39 as shown in FIG. 26.

Furthermore, the present embodiment has been described in the context ofa single light-emitting element 36 being disposed on the base 35, butthe number of the light-emitting elements is not limited to a particularnumber, and it is possible to employ, for example, a configuration inwhich three light-emitting elements 36 f, 36 g and 36 h are disposed onthe base 35 as shown in FIG. 27. It is also possible to employ, forexample, a configuration as shown in FIG. 28, in which twolight-emitting elements 36 f and 36 h are disposed on the base 35, and acover portion having a high refractive index (second cover portion 38 a)is disposed between the light-emitting elements 36 f and 36 h. When thespacing between the light-emitting elements is relatively large, thedistribution of primary light can be made uniform, and thus effectssimilar to those obtained in the example of Embodiment 8 described above(see FIG. 22) can be obtained such as realization of a thin surfacelight source.

Embodiment 10

A light-emitting device according to Embodiment 10 of the presentinvention will be described next with reference to FIG. 29. FIG. 29 is aschematic cross-sectional view showing an example of the light-emittingdevice according to Embodiment 10 of the present invention.

As shown in FIG. 29, a light-emitting device 53 of the presentembodiment includes a flat plate-like base 35 a, and a singlelight-emitting element 36 that is disposed on the base 35. Thelight-emitting element 36 is covered with a first cover portion 37 b ina tight contact state, and the side face of the first cover portion 37 bis surrounded by a second cover portion 38 b in a tight contact state.Furthermore, the first and second cover portions 37 b and 38 b arecovered with a wavelength converting portion 39 a in a tight contactstate. The wavelength converting portion 39 a has a uniform thickness,and a wavelength converting material constituting the wavelengthconverting portion 39 a is distributed uniformly.

The refractive index of the second cover portion 38 b is set higher thanthe refractive index of the first cover portion 37 b. In other words, inthe light-emitting device 53 of the present embodiment, the coverportion (the second cover portion 38 b) in the outer periphery of thewavelength converting portion 39 a has a refractive index higher thanthat of the other portion of the cover portion (the first cover portion37 b).

The configuration of the light-emitting device 53 of the presentembodiment also can provide effects similar to those obtained in thecase of the light-emitting device 34 of Embodiment 8 described above.

In the light-emitting device 53 of the present embodiment, thewavelength converting portion 39 a is formed into a dome shape, and thefirst and second cover portions 37 b and 38 b are formed into ahemisphere to fit into the dome shape of the wavelength convertingportion 39 a. According to this configuration, most of the light emittedfrom the light-emitting element 36 is incident upon the wavelengthconverting portion 39 a perpendicularly to the wavelength convertingportion 39 a, and it is therefore possible to prevent the reflection oflight at the interface between the wavelength converting portion 39 aand the first and second cover portions 37 b and 38 b. Thereby, thelight extraction efficiency can be further improved.

Other configurations, such as the configuration and mounting method ofthe light-emitting element 36, and the material of each member, are thesame as those of the light-emitting device 34 of Embodiment 8 describedabove.

Also in the light-emitting device 53 of the present embodiment, it ispreferable that a portion of the wavelength converting portion 39 a thatis located above the portion of the cover portion having a highrefractive index (the second cover portion 38 b) has a refractive indexhigher than that of the other portion of the wavelength convertingportion 39 a (the border between the regions having different refractiveindexes is indicated by dashed lines in FIG. 29).

The present embodiment has been described in the context of the basebeing a flat plate-like base 35 a, but the present embodiment is notnecessarily limited to the use of a base having this configuration, andit is also possible to use, for example, a base having a recess similarto those used in Embodiments 8 and 9 described above.

The present embodiment also has been described in the context of thefirst and second cover portions 37 b and 38 b being covered with thewavelength converting portion 39 a in a tight contact state, but it isalso possible to provide a space 40 a between the first and second coverportions 37 b and 38 b and the wavelength converting portion 39 a asshown in FIG. 30.

Furthermore, the present embodiment has been described in the context ofa single light-emitting element 36 being disposed on the base 35 a, butthe number of the light-emitting elements is not limited to a particularnumber, and it is possible to employ, for example, a configuration inwhich two light-emitting elements 36 i and 36 j are disposed on the base35 a as shown in FIG. 31.

Embodiment 11

A light-emitting device according to Embodiment 11 of the presentinvention will be described next with reference to FIG. 32. FIG. 32 is aschematic cross-sectional view showing an example of the light-emittingdevice according to Embodiment 11 of the present invention.

As shown in FIG. 32, a light-emitting device 54 of the presentembodiment includes a flat plate-like base 35 a, and a light-emittingelement 36 k that is disposed on the base 35 a. The light-emittingelement 36 k is covered with a cover portion 41 in a tight contactstate. Here, the cover portion 41 is formed by a first cover portion 37c that is disposed on the upper surface of the light-emitting element 36k, and a second cover portion 38 c that surrounds tightly the side faceof the light-emitting element 36 k and the side face of the first coverportion 37 c. Here, the first and second cover portions 37 c and 38 care formed such that their upper surfaces are flush with each other.Furthermore, the first and second cover portions 37 c and 38 c arecovered tightly with a wavelength converting portion 39 b. In thepresent embodiment, at least a portion of the wavelength convertingportion 39 b that is located above the first and second cover portions37 c and 38 c has a uniform thickness, and a wavelength convertingmaterial constituting the wavelength converting portion 6 is distributeduniformly.

The refractive index of the second cover portion 38 c is set higher thanthe refractive index of the first cover portion 37 c. In other words, inthe light-emitting device 54 of the present embodiment, the coverportion (the second cover portion 38 c) in the outer periphery of thewavelength converting portion 39 b has a refractive index higher thanthat of the other portion of the cover portion (the first cover portion37 c).

The configuration of the light-emitting device 54 of the presentembodiment also can provide effects similar to those obtained in thecase of the light-emitting device 34 of Embodiment 8 described above.

Other configurations, such as the configuration and mounting method ofthe light-emitting element 36 k, and the material of each member, arethe same as those of the light-emitting device 34 of Embodiment 8described above.

Similar to the case of Embodiment 10 given above, in the presentembodiment also, the wavelength converting portion 39 b may be formedinto a dome shape (see FIG. 33).

Also in the light-emitting device 54 of the present embodiment, it ispreferable that a portion of the wavelength converting portion 39 b thatis located above the portion of the cover portion having a highrefractive index (the second cover portion 38 c) has a refractive indexhigher than that of the other portion of the wavelength convertingportion 39 b (the border between the regions having different refractiveindexes is indicated by dashed lines in FIG. 32).

Embodiment 12

A light-emitting device according to Embodiment 12 of the presentinvention will be described next with reference to FIG. 34. FIG. 34 is aplan view showing an example of the light-emitting device according toEmbodiment 12 of the present invention.

As shown in FIG. 34, a light-emitting device 63 of the presentembodiment includes a flat plate-like base 60, and a plurality oflight-emitting elements 61 that are disposed on the base 60. Theplurality of light-emitting elements 61 are covered with a continuouswavelength converting portion 62. The plurality of light-emittingelements 61 are disposed such that the spacing between adjacentlight-emitting elements is decreased from the center portion side of thebase 60 gradually toward the periphery side thereof.

With the configuration of the light-emitting device 63 of the presentembodiment, it is also possible to provide a light-emitting device thatcan irradiate the irradiation surface with light of uniform color.

In the present embodiment, the plurality of light-emitting elements 61are disposed such that the spacing between adjacent light-emittingelements is decreased from the center portion side of the base 60gradually toward the periphery side thereof, but the present embodimentis not necessarily limited to this configuration. The plurality oflight-emitting elements 61 may be disposed such that the mountingdensity of the light-emitting elements 61 per unit area of thewavelength converting portion 62 is increased from the center portionside of the base 60 gradually toward the periphery side thereof. Evenwith this configuration, it is possible to provide a light-emittingdevice that can irradiate the irradiation surface with light of uniformcolor. Furthermore, the plurality of light-emitting elements 61 may bedisposed such that the light-emitting efficiency of the wavelengthconverting portion 62 is increased from the center portion side of thebase 60 gradually toward the periphery side thereof. Even with thisconfiguration, it is possible to provide a light-emitting device thatcan irradiate the irradiation surface with light of uniform color.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, it is possibleto provide a light-emitting device that can irradiate the irradiationsurface with light of uniform color by further reducing the light colordifference across the light extraction surface of the wavelengthconverting portion that covers the light-emitting element. Accordingly,the present invention is useful as a light source for displaybacklighting, a light source for sensors, a light source for thinlighting devices, and so on, that are required to be compact and thin.Furthermore, there is no particular limitation on the shape of theemitting surface. Besides a quadrangle which is commonly used, any shapecan be used such as a polygonal shape, circular shape, elliptic shape orstar-like shape.

1. A light-emitting device comprising a base, and a light-emittingelement that is disposed on the base and that emits primary light,wherein the light-emitting element comprises a plurality ofsemiconductor layers including a light-emitting layer, the lightemitting element is covered with a cover portion that includes a higherrefractive index portion having a refractive index higher than that ofan other portion of the cover portion, the higher refractive indexportion being located at an outer circumferential portion of the coverportion, the cover portion is covered with a wavelength convertingportion that includes a wavelength converting material that absorbs partof the primary light and emits secondary light, and a part of theprimary light emitted from the light-emitting element passes through theother portion of the cover portion and then through the higherrefractive index portion before entering the wavelength convertingportion.
 2. The light-emitting device according to claim 1, wherein atleast part of the cover portion includes a nanoparticle material, and atleast a portion of the cover portion in an outer periphery of thewavelength converting portion includes a nanoparticle material having arefractive index higher than that of a base material of the coverportion.
 3. The light-emitting device according to claim 1, wherein atleast part of the cover portion includes a nanoparticle material, and atleast a portion of the cover portion in an outer periphery of thewavelength converting portion includes a nanoparticle material at aratio higher than the other portion of the cover portion.
 4. Thelight-emitting device according to claim 1, wherein the wavelengthconverting portion is formed into a dome shape.
 5. The light-emittingdevice according to claim 1, wherein a portion of the wavelengthconverting portion that is located above a portion of the cover portionhaving a high refractive index has a refractive index higher than thatof the other portion of the wavelength converting portion.
 6. Thelight-emitting device according to claim 1, wherein a space is providedbetween the cover portion and the wavelength converting portion.
 7. Thelight-emitting device according to claim 1, wherein the wavelengthconverting portion has a substantially uniform thickness, and thewavelength converting material is dispersed substantially uniformly.